Change errors_out_migration decorator to work with RPC

This decorator in nova/compute/manager.py was written to work with
positional arguments, but at run time the decorated methods are
called via RPC with keyword arguments.  This change fixes the
decorator and the associated test cases.

Closes-Bug: #1300380

Change-Id: I9f87151a71e5217e7eff97cdc5cad2c85b620fa5
VMWare: add power off vm before detach disk during unrescue

Non Hot Plug type disk like IDE can only be detached when the VM is power off.

Change-Id: Ib1f387a41abe2b52357854e90c2535ebb7b43f18
Close-bug: #1279199
Merge "VMWare: add power off vm before detach disk during unrescue"
Merge "Change errors_out_migration decorator to work with RPC"