[Android] Fix make_apk fails to make arm packages

It's because in libs folder, arm folder is name
"armeabi-v7a" instead of "arm".
Fix by using a dictionary to convert cpu arch name to
cpu arch folder name.

BUG=https://crosswalk-project.org/jira/browse/XWALK-2272
Yes, this condition should never satisfied as you said. 
Just like native code `NOTIMPLEMENTED();`
It might be variable if something went wrong so that we can quickly locate the issue?