Fix outstanding failures with Neutron API job

Fix outstanding failures with Neutron API job

In order to run the API job successfully, must be installed and
configured. Today when using devstack-vm-gate.sh this means that
Tempest will run as well, which we do not want. To fix this problem
there are changes needed both in project-config and devstack-gate.

As a stop-gap solution, we bring in the scripts required and run
them directly within the gate hooks that we already have.

Once changes in devstack-gate and project-config will be accepted, this
solution can be dropped.

Supports-blueprint: retargetable-functional-testing

Change-Id: If04641ca6a12e956d7baff427e50816fd1a65fbe