Stop vm_state reset on reboot of rescued vm

When a VM is in rescue mode, giving it a reboot will reset its state in
the DB back to ACTIVE.

This patch stops that happening.

Work towards bug: 1170237
Change-Id: Ie442bcc85ed7ad5d897b88ffd0dbcf6eeee7b990
Adds tests to xenapi.vm_utils's 'lookup' method

Change-Id: I140f091b50c3e4076d3f4812cae00e37f120a277
Merge "Stop vm_state reset on reboot of rescued vm"
Merge "Adds tests to xenapi.vm_utils's 'lookup' method"