Fix for leaked ssh master connections.

AbstractSSHHost is cleaning the ssh master connection and then
running "pkill" that opens a new master connection that is never
closed.

BUG=614270

Change-Id: Ib42e01e478260aa9e429f80e6aa492232ae614bf
Reviewed-on: https://chromium-review.googlesource.com/347070
Commit-Ready: Godofredo Contreras <godofredoc@chromium.org>
Tested-by: Godofredo Contreras <godofredoc@chromium.org>
Reviewed-by: Roshan Pius <rpius@chromium.org>
Reviewed-by: Dan Shi <dshi@google.com>
diff --git a/server/hosts/abstract_ssh.py b/server/hosts/abstract_ssh.py
index 8c8e042..4ee54c3 100644
--- a/server/hosts/abstract_ssh.py
+++ b/server/hosts/abstract_ssh.py
@@ -681,9 +681,9 @@
 
     def close(self):
         super(AbstractSSHHost, self).close()
+        self.rpc_server_tracker.disconnect_all()
         self._cleanup_master_ssh()
         os.remove(self.known_hosts_file)
-        self.rpc_server_tracker.disconnect_all()
 
 
     def _cleanup_master_ssh(self):