Adds single NIC support for baremetal deployments

Simply use a new argument "-single_baremetal_nic <nic name>" to define which NIC to
bridge to on your host.  Also ensure when using this arg that your
ksgen_settings file has mac_address and private_mac as the same value
for your controllers (since you are using a single interface).

JIRA: APEX-33

Change-Id: I69095ccc4b907ae3c6ea3e88b2d1c9af9894c5cb
Signed-off-by: Tim Rozet <trozet@redhat.com>