When 'keystone token-get' fails, the caller can't detect the failure.
This cause troulbe shooting a bit complicated.
Change-Id: I3c58c5fd0e92a87e87546ea797904e08646a1097
Closes-Bug: #1238412
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