Add credentials and profile support to Neutron client

Add support to the Neutron client for credentials and profiles to allow
for working with Nexus 1000V. These are in support of the Nexus 1000V
Cisco plugin work.

Change-Id: I63e7ea09b1da027e308e32ae9a8e0400ab5965f2
Implements: blueprint cisco-n1k-neutron-client