add support for testing easyconfig PRs from eb command line

example usage (see also https://github.com/hpcugent/easybuild-easyconfigs/pull/857#issuecomment-42565991):

```
$ eb --test-easyconfigs-pr=857 --robot --github_user=jenkins1 --force
== temporary log file in case of crash /tmp/easybuild-FqdQKW/easybuild-1aiA1p.log
== resolving dependencies ...
== processing EasyBuild easyconfig /tmp/easybuild-FqdQKW/files_pr857/SOAPaligner-2.21_Linux-x86_64.eb
== building and installing SOAPaligner/2.21_Linux-x86_64...
== fetching files...
== creating build dir, resetting environment...
== unpacking...
== patching...
== preparing...
== configuring...
== building...
== testing...
== installing...
== taking care of extensions...
== packaging...
== postprocessing...
== sanity checking...
== cleaning up...
== creating module...
== COMPLETED: Installation ended successfully
== Results of the build can be found in the log file /user/scratchdelcatty/gent/vsc400/vsc40023/easybuild_REGTEST/SL6/sandybridge/software/SOAPaligner/2.21_Linux-x86_64/easybuild/easybuild-SOAPaligner-2.21-20140508.174314.log
== Build succeeded for 1 out of 1
== temporary log file /tmp/easybuild-FqdQKW/easybuild-1aiA1p.log has been removed.
== temporary directory /tmp/easybuild-FqdQKW has been removed.
== Test report, uploaded to https://gist.github.com/b7db9f056ef8eb2c83e8 and mentioned in a comment in easyconfigs PR#857:
Test result:
	Build succeeded for 1 out of 1 (1 easyconfigs in this PR)

Overview of tested easyconfigs (in order):
	[OK] SOAPaligner-2.21_Linux-x86_64.eb

Time info:
	start: Thu, 08 May 2014 15:43:00 +0000 (UTC)
	end: Thu, 08 May 2014 15:43:14 +0000 (UTC)

EasyBuild info:
	easybuild-framework version: 1.13.0dev
	easybuild-easyblocks version: 1.13.0dev
	command line:
		eb --test-easyconfigs-pr=857 --robot --github_user=jenkins1 --force
	full configuration (includes defaults):
		--buildpath=/user/home/gent/vsc400/vsc40023/.local/easybuild/build
		--config=/user/scratchdelcatty/gent/gvo000/gvo00002/vsc40023/easybuild_easy_installed/lib/python2.6/site-packages/easybuild_framework-1.13.0dev-py2.6.egg/easybuild/easybuild_config.py
		--disable-allow-modules-tool-mismatch
		--disable-avail-easyconfig-constants
		--disable-avail-easyconfig-licenses
		--disable-avail-easyconfig-params
		--disable-avail-easyconfig-templates
		--disable-avail-module-naming-schemes
		--disable-avail-modules-tools
		--disable-avail-repositories
		--disable-debug
		--disable-dry-run
		--disable-dry-run-short
		--disable-experimental
		--disable-ignore-osdeps
		--disable-info
		--disable-job
		--disable-list-toolchains
		--disable-logtostdout
		--disable-pretend
		--disable-quiet
		--disable-recursive-module-unload
		--disable-regtest
		--disable-regtest-online
		--disable-sequential
		--disable-set-gid-bit
		--disable-show-default-moduleclasses
		--disable-skip
		--disable-skip-test-cases
		--disable-sticky-bit
		--force
		--github_user=jenkins1
		--ignore-dirs=.git,.svn
		--installpath=/user/home/gent/vsc400/vsc40023/.local/easybuild
		--logfile-format=easybuild,easybuild-%(name)s-%(version)s-%(date)s.%(time)s.log
		--module-naming-scheme=EasyBuildModuleNamingScheme
		--moduleclasses=bio,chem,data,devel,ide,lib,mpi,perf,system,tools
		--modules-tool=EnvironmentModulesC
		--oldstyleconfig
		--repository=FileRepository
		--repositorypath=/user/home/gent/vsc400/vsc40023/.local/easybuild/ebfiles_repo
		--robot=/user/scratch/gent/vsc400/vsc40023/easybuild_easy_installed/lib/python2.6/site-packages/easybuild_easyconfigs-1.13.0.0dev-py2.6.egg/easybuild/easyconfigs
		--sourcepath=/user/home/gent/vsc400/vsc40023/.local/easybuild/sources
		--strict=warn
		--subdir-modules=modules
		--subdir-software=software
		--test-easyconfigs-pr=857
		--tmp-logdir=/tmp

System info:
	core_count: 16
	cpu_model: Intel(R) Xeon(R) CPU E5-2670 0 @ 2.60GHz
	cpu_speed: 2600.175
	cpu_vendor: Intel
	gcc_version: gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-4); Copyright (C) 2010 Free Software Foundation, Inc.; This is free software; see the source for copying conditions.  There is NO; warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.; ; 
	hostname: node2154.delcatty.os
	kernel_name: Linux
	libc_version: ldd (GNU libc) 2.12; Copyright (C) 2010 Free Software Foundation, Inc.; This is free software; see the source for copying conditions.  There is NO; warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.; Written by Roland McGrath and Ulrich Drepper.; 
	os_name: SL
	os_type: Linux
	os_version: 6.5
	platform_name: x86_64-unknown-linux
	python_version: 2.6.6 (r266:84292, Jan 22 2014, 05:06:49) ; [GCC 4.4.7 20120313 (Red Hat 4.4.7-3)]
	system_gcc_path: /usr/bin/gcc
	system_python_path: /usr/bin/python

List of loaded modules:
	cluster/delcatty

Environment:
	EASYBUILDBUILDPATH: /tmp/vsc40023/easybuild_build
	EASYBUILDPREFIX: /user/scratchdelcatty/gent/vsc400/vsc40023/easybuild_REGTEST/SL6/sandybridge
	EASYBUILDSOURCEPATH: /user/data/gent/vsc400/vsc40023/EasyBuild/sources:/apps/gent/source:/nfsmuk/apps/gent/source/
	G_BROKEN_FILENAMES: 1
	HISTCONTROL: ignoredups
	HISTSIZE: 1000
	HOME: /user/home/gent/vsc400/vsc40023
	HOSTNAME: node2154.delcatty.os
	LANG: en_US.utf8
	LC_ALL: en_US.utf8
	LC_CTYPE: UTF-8
	LESSOPEN: |/usr/bin/lesspipe.sh %s
	LOADEDMODULES: cluster/delcatty
	LOGNAME: vsc40023
	LS_COLORS: 
	MAIL: /var/spool/mail/vsc40023
	MODULEPATH: /etc/modulefiles/vsc:/user/scratchdelcatty/gent/vsc400/vsc40023/easybuild_REGTEST/SL6/sandybridge/modules/all
	MODULESHOME: /usr/share/Modules
	PATH: /user/home/gent/vsc400/vsc40023/lmod/5.1.5/libexec:/user/home/gent/vsc400/vsc40023/bin:/usr/local/bin:/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin:/opt/ibutils/bin:/user/scratch/gent/vsc400/vsc40023/easybuild_easy_installed/bin:/user/home/gent/vsc400/vsc40023/scratch/easybuild_easy_installed/bin
	PBS_DEFAULT: master15.delcatty.gent.vsc
	PWD: /user/home/gent/vsc400/vsc40023
	PYTHONPATH: /user/scratch/gent/vsc400/vsc40023/easybuild_easy_installed/lib/python2.6/site-packages:/user/scratch/gent/vsc400/vsc40023/easybuild_easy_installed/lib64/python2.6/site-packages:/user/home/gent/vsc400/vsc40023/.local/lib/python2.6/site-packages:/user/home/gent/vsc400/vsc40023/scratch/easybuild_easy_installed/lib/python2.6/site-packages:/user/home/gent/vsc400/vsc40023/scratch/easybuild_easy_installed/lib64/python2.6/site-packages
	SHELL: /bin/bash
	SHLVL: 2
	SSH_CLIENT: 172.24.13.3 42501 22
	SSH_CONNECTION: 172.24.13.3 42501 172.24.12.154 22
	SSH_TTY: /dev/pts/0
	TERM: xterm-256color
	USER: vsc40023
	VSCPROFILELOADED: 1
	VSC_ARCH_LOCAL: sandybridge
	VSC_DATA: /user/data/gent/vsc400/vsc40023
	VSC_DATA_VO: /user/data/gent/gvo000/gvo00002
	VSC_DATA_VO_USER: /user/data/gent/gvo000/gvo00002/vsc40023
	VSC_HOME: /user/home/gent/vsc400/vsc40023
	VSC_INSTITUTE: gent
	VSC_INSTITUTE_CLUSTER: delcatty
	VSC_INSTITUTE_LOCAL: gent
	VSC_OS_LOCAL: SL6
	VSC_SCRATCH: /user/scratch/gent/vsc400/vsc40023
	VSC_SCRATCHGULPIN: /user/scratchgulpin/gent/vsc400/vsc40023
	VSC_SCRATCH_CLUSTER: /user/scratchdelcatty/gent/gvo000/gvo00002/vsc40023
	VSC_SCRATCH_DELCATTY: /user/scratchdelcatty/gent/vsc400/vsc40023
	VSC_SCRATCH_DELCATTY_VO: /user/scratchdelcatty/gent/gvo000/gvo00002
	VSC_SCRATCH_DELCATTY_VO_USER: /user/scratchdelcatty/gent/gvo000/gvo00002/vsc40023
	VSC_SCRATCH_GENGAR: /user/scratchgengar/gent/vsc400/vsc40023
	VSC_SCRATCH_GENGAR_VO: /user/scratchgengar/gent/gvo000/gvo00002
	VSC_SCRATCH_GENGAR_VO_USER: /user/scratchgengar/gent/gvo000/gvo00002/vsc40023
	VSC_SCRATCH_GULPIN: /user/scratchgulpin/gent/vsc400/vsc40023
	VSC_SCRATCH_GULPIN_VO: /user/scratchgulpin/gent/gvo000/gvo00002
	VSC_SCRATCH_GULPIN_VO_USER: /user/scratchgulpin/gent/gvo000/gvo00002/vsc40023
	VSC_SCRATCH_NODE: /local
	VSC_SCRATCH_SITE: /user/scratch/gent/vsc400/vsc40023
	VSC_SCRATCH_VO: /user/scratch/gent/gvo000/gvo00002
	VSC_SCRATCH_VO_USER: /user/scratch/gent/gvo000/gvo00002/vsc40023
	VSC_VO: gvo00002
	_: /usr/bin/python
	_LMFILES_: /etc/modulefiles/vsc/cluster/delcatty
	module: () {  eval `/usr/bin/modulecmd bash $*`
}

```