Merge pull request #1269 from junmin-zhu/reduce

[Android] Refine the test cases to reduce time consumption.
[Android] Add arch option for packaging tool in embedded mode.

Accept the arch option from developer for embedded mode. if the arch
option is unspecified, all available platform apks will be generated.

Usage: python make_apk.py --arch=x86 ...

BUG=https://crosswalk-project.org/jira/browse/XWALK-598