[Android] Fix app packaging tool can't return its version.

The issue is due to the wrong directory it's stored. Put
VERSION file in the root target directory. Besides, a new test
case is added to check this issue.

BUG=https://crosswalk-project.org/jira/browse/XWALK-737
Merge pull request #1381 from yongsheng/fix737

[Android] Fix app packaging tool can't return its version.