Add libuv plugin

See also: http://review.couchbase.org/27740

Change-Id: I2589dee2647b15f06f02c4329de993b1c3552f23
Reviewed-on: http://review.couchbase.org/27741
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>