Android Windows: Adjust to new SDK layout

Google moved dx.bat into a new build-tools/VERSION folder
meaning our dx.bat no longer found dx.jar. Fix this by
passing into our dx.bat, the location of the real dx.bat

Removed hardcoded 17.0.0 and %ANDROID_BUILD_TOOLS_REVISION%
path searches.

Change-Id: I91c12c01745d6f12edbd126102b8f06eba291402
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>