MB-29287: Avoid ambiguity in ActiveStream cursor name

Handle the possible edge-case where the user-provided node-name plus
counter could be ambiguous - from Aliaksey:

    Consider the following case. Lets say we replicate to two nodes
    here, one named 'node' the other one 'node1'. We create
    replication to node1 and the counter is 0. Then after some time
    replication to node is created when the counter is 10. Now you
    have two totally different replications using the same cursor.

    ns_server happens to put the bucket name in the end of the
    connection name. So it saves us from the case I described. But a
    malicious client could craft a name that causes this sort of
    conflict.

This is very unlikely to occur, but not impossible; so for the sake of
being completeness avoid this situation by inserting a fixed seperator
between the user-provided name and the counter.

Change-Id: Ie308a09d420d8275ed059e834c09684675f9f737
Reviewed-on: http://review.couchbase.org/93407
Well-Formed: Build Bot <[email protected]>
Reviewed-by: Trond Norbye <[email protected]>
Reviewed-by: Daniel Owen <[email protected]>
Reviewed-by: Tim Bradgate <[email protected]>
Tested-by: Build Bot <[email protected]>

Author: daverigby

src/dcp/stream.cc

@@ -183,7 +183,7 @@ ActiveStream::ActiveStream(EventuallyPersistentEngine* e, dcp_producer_t p,
        payloadType((flags & DCP_ADD_STREAM_FLAG_NO_VALUE) ? KEY_ONLY :
                                                             KEY_VALUE),
        lastSentSnapEndSeqno(0), chkptItemsExtractionInProgress(false),
-       cursorName(n + std::to_string(cursorUID.fetch_add(1))) {
+       cursorName(n + '/' + std::to_string(cursorUID.fetch_add(1))) {
     const char* type = "";
     if (flags_ & DCP_ADD_STREAM_FLAG_TAKEOVER) {
         type = "takeover ";