retryq: fill proper temporary pipeline fields

We only filled the CQ's "parent" field which apparently is not enough --
the 'instance' field of the subclased mc_SERVER field must also be
filled. We use this temporary pipeline as bridge by which command
handlers can gain access to the actual lcb_t being used.

Change-Id: Ib3236a99899b43ce33e1f50b6121cd49e3a17068
Reviewed-on: http://review.couchbase.org/38192
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>