Skip `bnd-maven-plugin` configuration when `bnd.skip` is present

When `bnd.skip` is present, the `bnd-maven-plugin` configuration still kicks in and causes a

```
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-install-plugin:3.1.1:install (default-install) on project log4j-transform-maven-shade-plugin-extensions: The packaging for this project did not assign a file to the build artifact
```

failure.