app launch test fixes and improvements

* fixed NPE when specified app name does not exist
* force stop package before starting, because some names may
  resolve into the same package
* ensure app is launched in the order as sepcified in command
  line
* fixed time recording: it should have been 'thisTime' as
  reported by ActivityManager, to be consistent with previous
  harness

Change-Id: I411a568580feef21821dcbe6ec15884f697af6fd