Get-With-Replica - fix lots of breakage

Untested code resulted in several crashes:

- Assign strategy properly
- Copy over header to packet buffer
- Assign opaque to header
- Fix incorrect loop logic with 'FIRST' strategy
- Fix bad conditional logic when checking if there are sufficient
  replicas

Change-Id: Iaaa743740c05377dd9e0ee6af534c4bd5a6e0db4
Reviewed-on: http://review.couchbase.org/38089
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>