Fix bad use of port numbers.

-1 is not a valid quint16 number. It gets converted to 65535, which is
a valid port number. So, instead, use port number 0 which isn't valid
(if you try to bind to it, the OS chooses a port for you).

Found by ICC
src/plugins/android/androidrunner.cpp(150): warning #68: integer conversion resulted in a change of sign

Change-Id: I7de033f80b0e4431b7f1ffff13fc4e4f0f7af445
Reviewed-by: BogDan Vatra <bogdan@kde.org>