MB-5307: don't allow duplicate nodes in apply_changes
MB-5307: don't allow duplicate nodes in apply_changes

This fixes bug introduced by the following merge
c58f1d76c012d61ecb298c50238ae4605ad4b273.

It wasn't failing anything visibly, but was applying vbucket filter
changes multiple times.

Change-Id: Icf9aca8cfbd127fe6be9efeb3a06cec67175fae7
Reviewed-on: http://review.couchbase.org/16830
Reviewed-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>

nimishzynga/ns_server,membase/ns_server,pavel-blagodov/ns_server,pavel-blagodov/ns_server,daverigby/ns_server,nimishzynga/ns_server,t3rm1n4l/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,vzasade/ns_server,vzasade/ns_server,mschoch/ns_server,pavel-blagodov/ns_server,nimishzynga/ns_server,ceejatec/ns_server,daverigby/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,membase/ns_server,mschoch/ns_server,vzasade/ns_server,ceejatec/ns_server,membase/ns_server,t3rm1n4l/ns_server,membase/ns_server,daverigby/ns_server,vzasade/ns_server,mschoch/ns_server,membase/ns_server,nimishzynga/ns_server,mschoch/ns_server,nimishzynga/ns_server,ceejatec/ns_server,membase/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,daverigby/ns_server,mschoch/ns_server,daverigby/ns_server,ceejatec/ns_server,nimishzynga/ns_server,pavel-blagodov/ns_server