Replace non-ovs_lib calls of run_vsctl with libary functions

There is already an OVSBridge.set_controller() function, so replace
calls to run_vsctl(['set-controller', ...]) with calls to
OVSBridge.set_controller().

This is also the only non-ovs_lib call to run_vsctl. This change
will also make it easier to abstract out the ovsdb-related code in
the future.

Change-Id: Ia5a3e2c759d2479a2e7088a2ab7db1d4e17d1ae2
Add functional test for l3-agent metadata proxy

This change add a functional test for l3-agent metadata proxy to
verify:

 * iptables redirection from 169.254.169.254:80
 * headers added by the neutron-ns-metadata-proxy
 * proxy to the metadata_socket by the neutron-ns-metadata-proxy

Change-Id: I16f1269644a56d932426daa3a89dd5a8f747b314
Merge "Replace non-ovs_lib calls of run_vsctl with libary functions"
Merge "Add functional test for l3-agent metadata proxy"