Android: Enable script to run single autotest

To make it easier to debug failures, adds the "testcase"
commandline option, which takes the name of the test to
run and then just runs this single test.

Change-Id: Ib202bb2a5dac889b6691f9c4d0620b3e0941cf3d
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>
Ensure that output is world readable on Android

On Android, we need to be able to get access to the output
file remotely, so we make it world-readable.

Task-number: QTBUG-32079
Change-Id: I0a53a952d03339c0f1a1316f38bd206075589bde
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>
Reviewed-by: Simo Fält <simo.falt@digia.com>
Fix clean-up code in Android autotest script

If the files directory is not world-readable as well as
writable, the "rm *" command will fail because it cannot list
the files to delete.

Task-number: QTBUG-32079
Change-Id: Idb32a2be3184b9ffc43d011136fcc6f2a2a01756
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>
Reviewed-by: Simo Fält <simo.falt@digia.com>