Change loopback IP to interface IP.

In rsyslog test, if the rsyslog client and collector service
are on the same node, loopback IP was being used to send out
the rsyslog messages.

Changed this to use the actual node IP/interface IP for rsyslog
client configuration, to make it similar to the rsyslog
provisioning logic.

Change-Id: I6f4ea71ce2688b63ebede549c16a6b8ebb255fd5
Merge "Change loopback IP to interface IP."