Make context mandatory when instantiating a RPC object

RPC objects should have a context within it, this patch is making passing
the context mandatory when instantiating the object and is a plumbing
work to remove passing the context later for things like create(),
refresh(), destroy() and save().

Partial-Bug: #1314732
Change-Id: If9b175fa874bcb96c77cf22d176f1111f450f796
Merge "Make context mandatory when instantiating a RPC object"