Added functions for get a ip on an instance

The cause of some gating failure looks like
because of getting ip address on instance.
However current exercise didn't log the return value.
In this commit, we add get_instance_ip function with
error hanlding support, and apply it on the execise.

Change-Id: I8e17ba68093faafe58a98eb780a032368eea38aa
Merge "Added functions for get a ip on an instance"