Fix sql migrate repo prefix check
Fix sql migrate repo prefix check

Without this patch, the test_migrate_repos_file_names_have_prefix test
may not necessarily check the latest migration in the repo but could be
checking a __pycache__ file or a .pyc bytecode file, which would cause
the test to pass even if the latest migration did not contain the
required expand/migrate/contract prefix[1]. This patch corrects the
issue by using the glob module to filter only valid python files to
check.

This issue was noticed when the test correctly caught an error in the
py27 unit test job[1] but erroneously let slide the issue in the py3
tests[2].

[1] https://aca43ed1a01d95dea0ee-dcdb6cbb330bdac08ffee1284f86c919.ssl.cf2.rackcdn.com/687753/2/check/openstack-tox-py27/f602c1f/testr_results.html.gz
[2] https://openstack.fortnebula.com:13808/v1/AUTH_e8fd161dc34c421a979a9e6421f823e9/zuul_opendev_logs_832/687753/2/check/openstack-tox-py37/8322cff/testr_results.html.gz

Change-Id: I636f420e8a0c274131281af1d5aae931c164d91d

mahak/keystone,openstack/keystone,openstack/keystone,mahak/keystone,mahak/keystone,openstack/keystone