Rename driver 'activate' method to 'create'.

This will change the driver API to be more in-line with the
'hpcs_action' states.

libra/worker/drivers/base.py

@@ -38,8 +38,8 @@ class LoadBalancerDriver(object):
         """ Add a server for which we will proxy. """
         raise NotImplementedError()
 
-    def activate(self):
-        """ Activate any changes made. """
+    def create(self):
+        """ Create the load balancer. """
         raise NotImplementedError()
 
     def suspend(self):