agent: on shutdown don't allow server reconnection (#2904)

When agent is stopped, don't allow reconnection. Previously this would
send a shutdown command to the management server which would put the
host state to Disconnected but then agent's reconnection logic may kick
in sometimes which would connect the agent to the management server
but then the agent process would terminate causing the host to be
put in Alert state (due to ping timeout or it waiting too long).

This fixes the issue by ensuring that when the agent is stopped, it
does not reconnect to the management server.

Signed-off-by: Rohit Yadav <rohit.yadav@shapeblue.com>

Author: yadvr

agent/src/com/cloud/agent/Agent.java

@@ -303,6 +303,7 @@ public void start() {
 
     public void stop(final String reason, final String detail) {
         s_logger.info("Stopping the agent: Reason = " + reason + (detail != null ? ": Detail = " + detail : ""));
+        _reconnectAllowed = false;
         if (_connection != null) {
             final ShutdownCommand cmd = new ShutdownCommand(reason, detail);
             try {