Use stevedore aliases for interface_driver configuration

interface_driver configuration was updated to use stevedore aliases.
This patch is to change devstack scripts to now use the aliases
instead of the previous class imports.

Closes-Bug: #1504536

Change-Id: Ic56bfcc1f9da05a999e6fd328e4dd6617e9470ff
diff --git a/lib/neutron_plugins/openvswitch_agent b/lib/neutron_plugins/openvswitch_agent
index 48e47b3..5a843ff 100644
--- a/lib/neutron_plugins/openvswitch_agent
+++ b/lib/neutron_plugins/openvswitch_agent
@@ -110,7 +110,7 @@
 
 function neutron_plugin_setup_interface_driver {
     local conf_file=$1
-    iniset $conf_file DEFAULT interface_driver neutron.agent.linux.interface.OVSInterfaceDriver
+    iniset $conf_file DEFAULT interface_driver openvswitch
 }
 
 function neutron_plugin_check_adv_test_requirements {