MB-11896: only set up active vbucket stream

cbstats vbucket-seqno will output both active and replica vbuckets.
So we need to use vbucketmap to figure out the active vbucket list
on a node in cluster and only create dcp steams for active vbuckets.

Change-Id: If6f002d1c8628ed7c6b4e96c09025670114b1c76
Reviewed-on: http://review.couchbase.org/40352
Tested-by: Bin Cui <bin.cui@gmail.com>
Reviewed-by: Steve Yen <steve.yen@gmail.com>