Make some python3 fixes to make the unittests pass:
* galaxy imports
* dictionary iteration in role requirements
* swap_stdout helper for unittests
* Normalize to text string in a facts.py function
* add tests for centos6, rhel6 and rhel7
* gen_distribution_version_testcase with python2.6
* remove unused imports
* fix redhat/vmware/... parsing
* add centos7 test case
Updated python module wrapper explode method to drop 'args' file next to module.
Both execute() and excommunicate() debug methods now pass the module args via file to enable debuggers that are picky about stdin.
Updated unit tests to use a context manager for masking/restoring default streams and argv.