[Android] Add '--target-dir' option for packaging tool

This request comes from the Eclipse integration support.
Packaging tool will move the output APKS to the target
directory specified by developer.

BUG=https://crosswalk-project.org/jira/browse/XWALK-1139
Merge pull request #1697 from jinbang/master

[Android] Add '--target-dir' option for packaging tool