CCBC-169 refactor HTTP layer to allow restart requests

Change-Id: Ia358ae5593552ccfded4530eaf25c17f908e5bc6
Reviewed-on: http://review.couchbase.org/29919
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>