Exit rpc_loop when SIGTERM is recieved in ovs-agent

Previously ovs-agent exited with exit code 1 after SIGTERM was received.
SIGTERM should shutdown agent gracefully and exit code should be 0.

Closes-Bug: #1334264
Change-Id: I23e81cee5ae9e9fdabbe1377420b0902f47be8a7
Use patch ports to interconnect integration/physical bridges

Use by default patch ports to interconnect the integration to
physical bridges for the openvswitch agent in order to increase
performance.

For ovs/kernel without ovs patch port support on kernel side, veths
can be used through the new option OVS.use_veth_interconnection.

Patch port support can be tested using:

    neutron-sanity-check --ovs_patch

DocImpact
Closes-Bug: #1285335
Change-Id: I47106e57bf5b23891d7bf43815959e0d10156fba
Add config for performance gate job

This rally scenario is intended to be run in OpenStack CI
by rally-dsvm-neutron-neutron job.

Implements: blueprint neutron-performance-gate-jobs
Closes-Bug: #1334434
Change-Id: If204f3dfc32933792d09fdc929c248fc3f17b0bc
Merge "Use patch ports to interconnect integration/physical bridges"
Merge "Add config for performance gate job"
Merge "Exit rpc_loop when SIGTERM is recieved in ovs-agent"