'cbepctl stop' command hangs when waiting to confirm Flusher is stopped on cluster with 0 mutations

Summary

cbepctl stop hangs waiting for confirmation from KV-Engine that the Flusher has been stopped, if there are no mutations occurring on the primary shard (shard 0). Note the Flusher has been stopped, the command-line tool just cannot detect this.

Steps to Reproduce

1. Run epctl against a cluster with the flusher running (e.g. a freshly stated node), and with no mutations in flight:

   $ /opt/couchbase/bin/cbepctl 10.112.190.101:11210 -u cbadminbucket -p password -b default stop

2. Observe that the command doesn't return.

Expected Results
The command should return, confirming persistence has been stopped:

$ /opt/couchbase/bin/cbepctl 10.112.190.101:11210  -u cbadminbucket -p password -b default stop

Persistence stopped

$

Actual Results
The command hangs. Ctrl-C'ing and retrying gives an error (EINVAL) as the flusher actually /has/ already been stopped.