Add ChannelActiveUsers and ChannelConcurrentUsers as configurable parameters.  Change the units of sleep time to seconds.

Change-Id: Ib3f721c5ce0c9d55fd0592538814de8ee180c783
Reviewed-on: http://review.couchbase.org/38133
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Reviewed-by: Li Yang <lichenyang2@gmail.com>
Tested-by: buildbot <build@couchbase.com>