Fix the jar-with-dependencies building.

[kiuby88]

The jar-with-dependencies of compute-basics module can not be executed.

The assembly descriptor is deleted and the jar is built using a predefined descriptor.

[demobox]

Thanks for this, @kiuby88! Unfortunately, the default "jar-with-deps" descriptor does not work because it does not correctly merge the META-INF/services files - it picks one of the META-INF/services files instead.

This breaks jclouds because it uses the META-INF/services files to determine which APIs and providers are available.

See e.g. this StackOverflow post.