Add try for lasthypervisor request

Fixes a bug whereby lasthypervisor would be empty because a VM had
never migrated before. This situation should never matter in an
actually-migrated VM since the ZK value would be set and as such
is simply discarded.

pvcd/NodeInstance.py

@@ -170,7 +170,11 @@ class NodeInstance():
         ansiiprint.echo('Restoring node {} to active service.'.format(self.name), '', 'i')
         zkhandler.writedata(self.zk_conn, { '/nodes/{}/domainstate'.format(self.name): 'ready' })
         for dom_uuid in self.s_domain:
+            try:
                 last_hypervisor = zkhandler.readdata(self.zk_conn, '/domains/{}/lasthypervisor'.format(dom_uuid))
+            except:
+                continue
+
             if last_hypervisor != self.name:
                 continue