Use default rpc_response_timeout in unit tests

During running of tox the system can timeout on slower systems.
We have seen this occur in our internal tests and have seen
better results when we increased the api timeout from 15 to 60
seconds.  This can be used until faster hardware is availale
or a better fix is proposed.  Andrew Laski first proposed
this fix.

Closes-Bug: 1311778

Change-Id: I33da328e7bea8fbdde3f01ee0147b4c5a3a278d2
(cherry picked from commit dead965a4398d5093426cf21d2875b55a451e671)
Merge "Use default rpc_response_timeout in unit tests" into stable/icehouse