Add version to scheduler rpc API.

Part of blueprint versioned-rpc-apis.

One side effect of this change was that cinder.scheduler.api was removed
in favor of cinder.scheduler.rpcapi.  In this case, the api was just a
direct wrapper around rpc usage.  For other APIs, I've been following
the pattern that the rpcapi module provides the rpc client wrapper, and
if any other client-side logic is needed, that's where an api module is
used.

Change-Id: Ibd0292936f9afc77aeb5d040660bfa857861eed1

cinder/scheduler/manager.py

@@ -47,6 +47,8 @@ FLAGS.register_opt(scheduler_driver_opt)
 class SchedulerManager(manager.Manager):
     """Chooses a host to run instances on."""
 
+    RPC_API_VERSION = '1.0'
+
     def __init__(self, scheduler_driver=None, *args, **kwargs):
         if not scheduler_driver:
             scheduler_driver = FLAGS.scheduler_driver
@@ -55,6 +57,9 @@ class SchedulerManager(manager.Manager):
 
     def __getattr__(self, key):
         """Converts all method calls to use the schedule method"""
+        # NOTE(russellb) Because of what this is doing, we must be careful
+        # when changing the API of the scheduler drivers, as that changes
+        # the rpc API as well, and the version should be updated accordingly.
         return functools.partial(self._schedule, key)
 
     def get_host_list(self, context):