Fail when Android bytecode compilation fails

[FilipeMarch]

Summary

Fail the Android Gradle build when Python bytecode compilation fails.

Problem

The generated OptimizePythonTask ran compileall but ignored its exit code.
It then deleted the Python source files regardless of the result.

This could produce an APK without required .pyc files. At runtime Python
failed during initialization with:

  failed to get the Python codec of the filesystem encoding

Changes

• Capture the compiler output.
• Print compiler errors in the Gradle log.
• Check the compileall exit code.
• Abort the build before deleting .py files when compilation fails.
• Add a regression test for the generated Gradle template.

Validation

• Focused regression test passed.
• Python compilation checks passed.

[Novfensec]

@psychowasp We should merge this.