Fix missing removal of directories for MkDirOperation

 * use removeDirectory instead of rmdir
 * rmdir is not able to delete subdirectories
 * pass force parameter to removeDirectory
 * adds unit test

Change-Id: I1f52aefdb5d13793321fe6001809362d34ad8941
Reviewed-by: Niels Weber <niels.weber@digia.com>
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>