MINOR: master/cli: also implement the timed prompt on the master CLI

MINOR: master/cli: also implement the timed prompt on the master CLI

This provides more consistency between the master and the worker. When
"prompt timed" is passed on the master, the timed mode is toggled. When
enabled, for a master it will show the master process' uptime, and for
a worker it will show this worker's uptime. Example:

  master> prompt timed
  [0:00:00:50] master> show proc
  #<PID>          <type>          <reloads>       <uptime>        <version>
  11940           master          1 [failed: 0]   0d00h02m10s     2.8-dev11-474c14-21
  # workers
  11955           worker          0               0d00h00m59s     2.8-dev11-474c14-21
  # old workers
  11942           worker          1               0d00h02m10s     2.8-dev11-474c14-21
  # programs

  [0:00:00:58] master> @!11955
  [0:00:01:03] 11955> @!11942
  [0:00:02:17] 11942> @
  [0:00:01:10] master>