test_python_cmd_build fails in offline VM build

[jayvdb]

It would be nice if these tests where given a skipable marker, like 'online', so pytest -k 'not online' works.

A nice online check is whether name github.com can be resolved.

In the meantime pytest -k 'not test_python_cmd_build' wfm.

[   31s] E           subprocess.CalledProcessError: Command '['git', 'clone', 'https://github.com/kevinconway/rpmvenv.git', '/tmp/pytest-of-abuild/pytest-0/test_python_cmd_build_https___3/rpmvenv']' returned non-zero exit status 128.
[   31s] 
[   31s] /usr/lib64/python3.6/subprocess.py:291: CalledProcessError
[   31s] ---------------------------- Captured stderr setup -----------------------------
[   31s] Cloning into '/tmp/pytest-of-abuild/pytest-0/test_python_cmd_build_https___3/rpmvenv'...
[   31s] fatal: unable to access 'https://github.com/kevinconway/rpmvenv.git/': Could not resolve host: github.com
[   31s] =========================== short test summary info ============================
[   31s] ERROR tests/test_cli.py::test_python_cmd_build[https://github.com/kevinconway/rpmvenv.git-python2.7-False-True-True]
[   31s] ERROR tests/test_cli.py::test_python_cmd_build[https://github.com/kevinconway/rpmvenv.git-python2.7-False-True-False]
[   31s] ERROR tests/test_cli.py::test_python_cmd_build[https://github.com/kevinconway/rpmvenv.git-python2.7-False-False-True]
[   31s] ERROR tests/test_cli.py::test_python_cmd_build[https://github.com/kevinconway/rpmvenv.git-python2.7-False-False-False]