The vm_state should not be modified until the task is complete.

Several methods in nova.compute.api alter the vm_state value before
proceeding with the actual work. The initial vm_state may be changed to
something other than the initial vm_state (which is a problem: since we
do not know what the initial state actually was, we cannot reasonably
recover and set the corresponding ERROR if a problem with the operation
occurs).

Actually done:

Removed vm_state update before executing task

Changed methods:
- reboot
- pause
- unpause
- suspend
- resume
- rescue
- unrescue

Fixes: bug #1158509
Change-Id: I5ee7aebf3c4831dd577ed5ab9aa155095152f8a8
Update run_tests.sh to run flake8 too.

Change-Id: I6fce8ef0a293fb92c7e0ceb4ef88284e93022b54
Merge "The vm_state should not be modified until the task is complete."