update query monitoring docs with info about the user cbq-engine-cbauth

Cbq-engine is a new (spock) internal user that ns_server uses to allow QWB clients to query across multiple query nodes.

Recall that QWB can only connect to the same node as cqb-engine is running? The offshoot of this is that QWB cannot do any query clustered operations.

To get round this once QWB clients connect to a query node, this internal user will be used to do any further inter node user verification.

HTH,

Marco

From: Fujio Turner <Fujio.Turner@couchbase.com>
**

Query team,

 Is the below user a query node. Found this is the http_access_internal.log

@cbq-engine-cbauth [03/Jul/2017:06:45:30 +0000] "GET /pools/default/buckets/Transport/ddocs HTTP/1.1" 200 1254 - Go 1.1 packagehttp

who is this user @cbq-engine-cbauth ?

Thank you,