Automatically set availability_zone in Volume

In the Volume cinderlib object we store the backend in the
availability_zone field and we were passing this field on the
Backend.create_volume method to the objects.Volume.

This patch changes this so the create_volume doesn't have to care about
it and it's the Volume.__init__ method that takes care of setting the
field for all sources (kwargs, volume, ovo).

cinderlib/cinderlib.py

@@ -103,7 +103,7 @@ class Backend(object):
                       **kwargs):
         vol = objects.Volume(self, size=size, name=name,
                              description=description, bootable=bootable,
-                             availability_zone=self.id, **kwargs)
+                             **kwargs)
         vol.create()
         return vol
 

cinderlib/objects.py

@@ -200,10 +200,12 @@ class Volume(NamedObject):
     def __init__(self, backend_or_vol, **kwargs):
         # Accept backend name for convenience
         if isinstance(backend_or_vol, six.string_types):
+            kwargs.setdefault('availability_zone', backend_or_vol)
             backend_or_vol = self.backend_class.backends[backend_or_vol]
-
+        elif isinstance(backend_or_vol, self.backend_class):
+            kwargs.setdefault('availability_zone', backend_or_vol.id)
         # Accept a volume as additional source data
-        if isinstance(backend_or_vol, Volume):
+        elif isinstance(backend_or_vol, Volume):
             # Availability zone (backend) will be the same as the source
             kwargs.pop('availability_zone', None)
             for key in backend_or_vol._ovo.fields: