Moved libuv plugin to couchnode.

This change is due to the need to have access to node
specific  details for version-specific building to
support node v0.11.

Change-Id: Ice9aeadf471616ae82433f226479c64faffa0150
Reviewed-on: http://review.couchbase.org/30477
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Brett Lawson <brett19@gmail.com>