Allow abort of shutdown state

Adds some logic to allow an active shutdown state to be aborted by
changing the VM to another state. Useful mostly if a VM is doing funky
things and not responding to the shutdown, but the administrator either
doesn't want to wait for the timer to expire (forcing an immediate
termination) or wishes to abort the shutdown attempt.

Fixes #49

node-daemon/pvcd/VMInstance.py

@@ -229,12 +229,20 @@ class VMInstance(object):
     # Shutdown the VM gracefully
     def shutdown_vm(self):
         self.logger.out('Gracefully stopping VM', state='i', prefix='Domain {}:'.format(self.domuuid))
+        is_aborted = False
         self.inshutdown = True
         self.dom.shutdown()
         tick = 0
         while True:
-            tick += 1
-            time.sleep(1)
+            tick += 2
+            time.sleep(2)
+
+            # Abort shutdown if the state changes to start
+            current_state = zkhandler.readdata(self.zk_conn, '/domains/{}/state'.format(self.domuuid))
+            if current_state != 'shutdown':
+                self.logger.out('Aborting VM shutdown due to state change', state='i', prefix='Domain {}:'.format(self.domuuid))
+                is_aborted = True
+                break
 
             try:
                 lvdomstate = self.dom.state()[0]
@@ -258,6 +266,9 @@ class VMInstance(object):
 
         self.inshutdown = False
 
+        if is_aborted:
+            self.manage_vm_state()
+
         if self.inrestart:
             # Wait to prevent race conditions
             time.sleep(1)