Fix heat template for cassandra

Reasons:
 - heat template for cassandra misses OS::Neutron::Port resource which is 
   required for NICs that can be applied to an instance.

Changes:
 - adding OS::Neutron::Port cassandra heat template.

Change-Id: I9661ae5d6e0695b7fd56d97cc6cd6ab874a3b5d0
Closes-Bug: #1308131
Merge "Fix heat template for cassandra"