ProjectExplorer: Improve 'ps' output parsing.

- Get rid of distinction between Mac and other Unices. Instead,
  use POSIX syntax that should work on all compliant systems
  (tested on OSX and Linux).
- Actually extract command instead of just setting it to
  the same value as the whole command line. This is not correct in the
  presence of spaces in the command, but better than before.

Change-Id: Ie25155688e0e9bbe0d45cde20563929b7370695d
Reviewed-by: hjk <hjk121@nokiamail.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>