Add nova_ca_certificates_file option to neutron

Previously, neutron had no way to pass a certificates file to the
novaclient.  This change is to add that ability, similar to the way
you can pass a certificates file to neutronclient in nova.conf via
neturon_ca_certificates_file.

Change-Id: I1a3f85505eb44bee604900301af79d773e1952a3
Closes-Bug: #1309694
Merge "Add nova_ca_certificates_file option to neutron"