input: added support for multiple keyevents

- Multiple keyevents can now be send from the command line:

    input keyevent <key code number or name> ...

  Sometimes invoking 'input' repeatedly does not send the events fast
  enough, this change solves the problem by allowing multiple key code
  number or names be added to the command line.

Change-Id: I0d0f34bddd99e0195c9badff2f8b3e2aa9a51737