Reject connection if client has a different cluster name

[mgmacias95]

Hello team,

This PR fixes #803.

The error shown in the master node is:

# /var/ossec/bin/wazuh-clusterd -f
2018-07-04 04:24:52,047 INFO    : [Master] PID: 12853
2018-07-04 04:24:52,048 INFO    : [Master] Listening '0.0.0.0:1516'.
2018-07-04 04:24:52,293 ERROR   : [Transport-ServerHandler] Error accepting connection from 192.168.185.7: Incoming connection from '192.168.185.7' rejected: cluster name is different (wazuh2/wazuh).
2018-07-04 04:24:52,293 INFO    : [Master] Connection with 192.168.185.7 closed.
2018-07-04 04:24:54,052 INFO    : [Master] [Internal-COM ]: Ready.
2018-07-04 04:25:03,241 ERROR   : [Transport-ServerHandler] Error accepting connection from 192.168.185.7: Incoming connection from '192.168.185.7' rejected: cluster name is different (wazuh2/wazuh).
2018-07-04 04:25:03,242 INFO    : [Master] Connection with 192.168.185.7 closed.
^C2018-07-04 04:25:13,629 INFO    : [Master] Exiting. Reason: 'Signal [2-Interrupt] received.'.

This is the output from a client node:

# /var/ossec/bin/wazuh-clusterd -f
2018-07-04 04:24:52,063 INFO    : [Client] PID: 2806
2018-07-04 04:24:52,186 INFO    : [Client] Connecting to 192.168.185.6:1516.
2018-07-04 04:24:52,187 INFO    : [Client] Connected.
2018-07-04 04:24:52,296 INFO    : [Client] Disconnected.
2018-07-04 04:24:52,296 ERROR   : [Client] Disconnected. Trying to connect again in 10s.
2018-07-04 04:24:54,067 INFO    : [Client] [Internal-COM ]: Ready.
2018-07-04 04:25:03,242 INFO    : [Client] Connecting to 192.168.185.6:1516.
2018-07-04 04:25:03,243 INFO    : [Client] Connected.
2018-07-04 04:25:03,244 INFO    : [Client] Disconnected.
2018-07-04 04:25:03,244 ERROR   : [Client] Disconnected. Trying to connect again in 10s.
^C2018-07-04 04:25:13,624 INFO    : [Client] Exiting. Reason: 'Signal [2-Interrupt] received.'.

Best regards,
Marta