Added initial support for systemd-networkd link configuration, now
you can configure and rename the name of a network interface if you
know the MAC address of the interface.

Also added unit tests and fixed issues in the test_overcloud_host_configure.py:
 * Added unit test for networkd.
 * Fixed pep8 issues.
 * Removed unused import.
 * Fixed 'not in' issue in assert.

Change-Id: I8321183dbc747ef521aa0d2660ebeef8b0342c6a
Signed-off-by: Maksim Malchuk <maksim.malchuk@gmail.com>