Add 'reset-state' to update trove server status in database

Problem:
As we know, trove will boot a server with status 'BUILD' waiting for heartbeat from trove-guestagent to update its status. But in some cases, trove-conductor did not update the state, for example, instance build error, trove-guestagent not work, or network problem and so on. When the state is 'BUILD', we can not delete the server through trove API and which may also effect tenant quota usage.

Solution:
nova and cinder have the same problem. They use 'reset-state' to change the status in database.
We can support 'reset-state' in trove API and troveclient to make it possible to update server status manually.