Fix getting empty "modules" directory when arch is not armeabi-v7a

[j-devel]

In create_python_bundle(), copy source path of built modules (*.so) is hardcoded to arm. This results in an empty modules directory when build arch is other than armeabi-v7a.

This PR fixes the above issue; accordingly, the modules directory is generated as expected (when arch is x86, x86_64,arm64-v8a, etc).

[AndreMiras]

One hardcoded arm less, well done!
It looks good even though playing with the command_prefix string feels a bit hacky, I didn't see what else we could use.
I've restart the build that was flaky and will merge if it goes green.
Thanks!

[AndreMiras]

Merged thanks!

[j-devel]

Thanks!

playing with the command_prefix string feels a bit hacky, I didn't see what else we could use.

Indeed. In future, if this arch.command_prefix.split('-')[0] stuff starts appearing multiple times in other part of code, I think it's time to consider refactoring it as a member/method of the Arch class.