Open port 8000 for heat-api-cfn for public neutron net

The heat-slow tests are currently failing because nova servers cannot
reach heat-api-cfn to signal waitconditions. This change is an attempt
to fix that.

Change-Id: I08c27dc569b86a73f5aa3ead48569e6a8161e980
Merge "Open port 8000 for heat-api-cfn for public neutron net"