tools/github/github_issues.py: Fix pylint problem

A new upstream version of github caught correctly
that self._issue_cache_key is not a method, but
a property. Fix that.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
virttest/qemu_devices_unittest.py: Remove enabling protected access

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
virttest/utils_config_unittest.py: Skip tests on libvirtd absence

Those tests are not strictly unit tests, rather, they
are functional tests, since they depend on libvirtd to
properly work. Let's skip them if libvirtd is not
available.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
Merge pull request #1787 from autotest/fix-travis

Fix travis