VM in rescue state must have a restricted set of actions

Right now it is possible to pause, suspend and stop a VM in state RESCUED,
so after the state is changed, it's not possible to trigger unrescue anymore
since the original state is lost.

This patch remove vm_states.RESCUED as valid state from stop,
pause and suspend actions.

The vm_states devref is also updated to reflect this change including the
current reboot flow.( vm_states.RESCUED cannot be rebooted as per
today code)

This is a backport of 8ff170dc95bf3101fe38a2624e941bfa3b7c1138 .

DocImpact
Closes-Bug: #1319182
Co-Authored-By: Cyril Roelandt <cyril.roelandt@enovance.com>
Change-Id: I531dea5a5499bf93c24bea37850d562134dee281
Merge "VM in rescue state must have a restricted set of actions" into stable/icehouse