MB-11828 upr client: Increase gen_server call timeout to 1 min

The default gen_server call timeout value of 5 seconds seems to be too low.
During rebalance, the upr client seems to be busy and results in timeout.
This impacts the rebalance and it fails during certain cases.

Change-Id: I7791060c26b01fd6f1b6d4afce370c37ad92bef6
Reviewed-on: http://review.couchbase.org/39984
Reviewed-by: Nimish Gupta <nimish@couchbase.com>
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>