[Android] make_apk: Use open(), not file().

The latter does not exist in Python 3, so those functions were broken
when invoked.

(cherry picked from commit f7d41a1eb5be7b4659098ac9d790f024267ab61b)
Merge pull request #2223 from rakuco/py3-compatibility-v7

[Android] make_apk: Use open(), not file().