xdcr test uses incorrect url to delete replication

which causes goxdcr to return 301
which breaks the test after applying the following commit to ns_server:
http://review.couchbase.org/61683

2016-03-18 18:06:50 | ERROR | MainProcess | test_thread | [rest_client._http_request] http://127.0.0.1:9000//controller/cancelXDCR/19bf71633438d55f2e70fb59d4ed88f8%2Fdefault%2Fdefault error 301 reason: status: 301, content:

Here's the redirect that goxdcr returns:
{301, [

{"Content-Type","text/plain; charset=utf-8"}

,

{"Date","Sat, 19 Mar 2016 01:28:02 GMT"}

,

{"Location", "/controller/cancelXDCR/19bf71633438d55f2e70fb59d4ed88f8/default/default"}

],
<<>>}