[CX] Connect link can fail w/ internal error if kv lagging with rbac updates

If CONNECT LINK on a remote link is executed immediately after creating a user or granting him DCP reader access, we may attempt to create the DCP connections before KV engine has processed the RBAC update(s)- this will result in an "Internal error" reported to the user.

We work around this in our dev tests by not issuing the CONNECT LINK until we see an RBAC update in the memcached logs.