Cherry-pick from branch_v2plus changing popen calls to use the subprocess module

Conflicts:

	factory/glideFactory.py
	frontend/glideinFrontend.py
	lib/condorExe.py
	lib/rrdSupport.py
Use strip() for trailing whitespace

Previously the code was just blindly slicing off the last character.
(noted during an strace when it was trying to exec /usr/bi/condor_status)
Moved iexe_cmd to subuprocessSupport and changed rest of the code to use it. Issue #2634
Convert argument list to string for use with subprocess. Issue #2634
Fix imports
Handle the difference in return value of poll subprocess. Popen returns None for running process
Do not use comparions operators when looking for None
Fixed a bunch of issues to accomodate subprocess
- convert command to utf8
- use strip() rather than slicing
- use full path to voms-proxy-info
- fixed return value of condorExe.iexe_cmd()
- pass environment to subprocess correctly rather than multi command line
Fixed truncated line
fixed typo
Use strip() to strip out white spaces
Bug #2634 Migrate popen calls to subprocess for SL6 compatibility

As a part of the change to use the subprocess module, the iexe_cmd
method in condorExe.py was changed to return the output using
splitlines which striping newlines characters.
The method that creates the frontend condor_config during "creation"
assumed newlines would exist. So the change was just to simply write
the existing condor attributes into the file in a 'for' loop.
Updated the issues to look out for when using subprocess.communicate