Vm state management and error states
Vm state management and error states

this implements the blueprint nova-vm-state-management
It implements the following functionalities:
- Filter compute api calls according to state of the VM
(defined in compute/state_checker).
- Sets error state if the scheduler cannot allocate the VM in any host
- Handles the create/delete concurrency in the compute manager

Change-Id: Ie6d016b7d4781f70bb5967f204fa88a6412bd727

n0ano/ganttclient