Support: --sources-dir or --source and --retrieve for --spec

Either supply a --sources-dir containing resources for spec
or supply list of tarballs using --source.

If --retrieve is passed after --spec, trigger spectool
to download resources inside the container.
Print errors from docker
Support: --config and --docker-<options>

docker client instance is now instantiated inside Packager where it is used
(should make testing easier when tests arrives)

Configuration values to docker client such as:
 * base_url to reach docker
 * version to communicate with API
 * timeout towards API

command line arguments for configuration (--docker-<options>)
overrides config defined in --config <file>.

Includes requirements-dev.txt for developers to install dev dependencies.
Also added into setuputils where to look for test suite(s).
Merge branch 'master' of https://github.com/norrs/docker-rpmbuild into norrs-master

Conflicts:
	rpmbuild/__init__.py
Merge branch 'norrs-master'
Making #4 compatible with home directory changes
Merge branch 'docker' of https://github.com/norrs/docker-rpmbuild into norrs-docker

Conflicts:
	rpmbuild/__init__.py
Python 3 compatibility
Using real temporary file for config tests
Merge branch 'norrs-docker'