Fix scheduling in retryq

1) Next tick delta was being calculated as seconds _before_ now. This
   should be seconds after now.
2) First operation timeout should take into account the actual timeout
   rather than just its start time.

Change-Id: Ia5058fa91be337c95f79f2156925ebb0d4741b84
Reviewed-on: http://review.couchbase.org/39256
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>