Previously interface_driver for q-lbaas is hardcoded and q-lbaas does
not work when quantum plugin requires additional configuration (like
ovs_use_veth=True). This commit set up interface_driver using
quantum_plugin_setup_interface_driver function.
This commit also moves a script related Quantum service plugin to
lib/quantum_plugins/services/
Change-Id: Iad11c1b31071dfb580843be18be78c83feb91f10