Check if node changed during final check

Avoids situations where two migrates, to different nodes, happen in
rapid succession. Aborts the migration if the current target node no
longer matches what was set at the start of the execution.

node-daemon/pvcnoded/VMInstance.py

@@ -353,6 +353,9 @@ class VMInstance(object):
         self.inmigrate = True
         self.logger.out('Migrating VM to node "{}"'.format(self.node), state='i', prefix='Domain {}'.format(self.domuuid))
 
+        # Used for sanity checking later
+        target_node = zkhandler.readdata(self.zk_conn, '/domains/{}/node'.format(self.domuuid))
+
         aborted = False
 
         def abort_migrate(reason):
@@ -455,6 +458,9 @@ class VMInstance(object):
         if self.node == self.lastnode or self.node == self.this_node.name:
             abort_migrate('Target node matches the current active node during final check')
             return
+        if self.node != target_node:
+            abort_migrate('Target node changed during preparation')
+            return
 
         # A live migrate is attemped 3 times in succession
         ticks = 0