Rebased our branches on latest p4a develop HEAD and buildozer master HEAD.
Re `android.allow_backup = False` in buildozer.spec, now that this setting
has been exposed to buildozer.spec (see https://github.com/kivy/buildozer/pull/1206),
we could finally drop a commit from our branch that did the same:
7a7d415d90
Re commenting out `android.arch` in buildozer.spec, we are setting this
via the ENV VAR in make_apk.
follow-up: 59e9337be0
For some reason, without this change, the first build works but subsequent builds fail.
Not sure what the cause is. This is why Travis builds work.
