Currently, "ansible localhost -m setup" can fail silently during the
run of gen_distribution_version_testcase.py, resulting in incorrect
output. Use check_output() rather than communicate() and handle
the exception if we get a nonzero return value.
As suggested in feedback on
https://github.com/ansible/ansible/pull/17575, add
os_family to test_distribution_version. Add the
correct os_family to the existing testcase data
entries.
Also add os_family to the output of
gen_distribution_version_testcase.py so any new
generated entries will contain this data.
* 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
