Monitor: Poll more often

Particulary for small runs, the current polling interval of 5s is
pretty generious, so reduce to 2s to we can detect a quiscient state
quicker.

(Note the MAX_RETRY value is adjusted to ensure that the total time we
are willing to wait for is still 60s).

Change-Id: Id87b7d700898865b0fc7fa2567e35ca80c20e150
Reviewed-on: http://review.couchbase.org/39947
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>