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/bigswitch_floodlight b/lib/neutron_plugins/bigswitch_floodlight
index 4166131..f52105e 100644
--- a/lib/neutron_plugins/bigswitch_floodlight
+++ b/lib/neutron_plugins/bigswitch_floodlight
@@ -58,9 +58,9 @@
 function neutron_plugin_setup_interface_driver {
     local conf_file=$1
     if [ "$BS_FL_VIF_DRIVER" = "ivs" ]; then
-        iniset $conf_file DEFAULT interface_driver neutron.agent.linux.interface.IVSInterfaceDriver
+        iniset $conf_file DEFAULT interface_driver ivs
     else
-        iniset $conf_file DEFAULT interface_driver neutron.agent.linux.interface.OVSInterfaceDriver
+        iniset $conf_file DEFAULT interface_driver openvswitch
     fi
 }