Wait for lock release during power state change

When power state change is slow, the subsequent provide workflow can
fail because getting a lock on the node times out.

Apparently a node can remain locked for some time after a power state
change, so this issue should be solved by *also* waiting for the node
to be unlocked in the wait_for_power_state action.

Change-Id: I26f23330c50ccf7cb11fb9171d0a82279a497d22
Closes-Bug: #1846791
(cherry picked from commit bc29d7f938)

workbooks/baremetal.yaml

@@ -84,12 +84,12 @@ workflows:
         action: ironic.node_get
         input:
           node_id: <% $.node_uuid %>
-          fields: ['power_state', 'last_error']
+          fields: ['power_state', 'last_error', 'reservation']
         timeout: 120 #2 minutes
         retry:
           delay: 6
           count: 20
-          continue-on: <% not task().result.power_state in [$.target_state, $.error_state] %>
+          continue-on: <% not (task().result.power_state in [$.target_state, $.error_state] and task().result.reservation = null)%>
         on-complete:
           - state_not_reached: <% task().result.power_state != $.target_state %>