Add context as parameter for resume

Now for KVM when resume an instance with block storage, nova
compute will throw exception and failed to resume the VM.

The root cause is that when resume a VM with block storage,
libvirt driver needs to call conductor via rpcapi to update
block device, but the function of resume() do not have context,
this will cause RPC api failed.

Change-Id: I712777ed1d893a2b6463d30c407b0a677e37b602
Closes-Bug: #1241337
Merge "Add context as parameter for resume"