[Android] Make make_apk work on Windows again.

This commit series includes fixes for some regressions in make_apk.py on
Windows introduced by pull request #2229. It uses a different approach
than #2381 for the fixes.

Quick summary:
* We call `android` and `ant` with full paths and a proper
  extension (like ".bat") since Windows does not call "foo.bat" if we
  use subprocess.Popen(["foo"]) with `shell=False`.
* We stop adding double quotes to the keystore arguments passed to Ant
  because they are passed literally on Windows and break when the values
  have spaces on Unix.

BUG=XWALK-2377