support all usual ROS setup features via _setup_util.py

[asmodehn]

Currently underlays are not supported.

Probably other features that people are used to have when sourcing setup.bash, are not supported when using pyros test.

We should find a way to detect the _setup_util.py module (present in all workspaces) and use it from pyros-setup, in order to provide all the features that setup.bash provides.

[asmodehn]

Actually underlays ARE supported by using "delay_import" directly, instead of the "delay_import_auto" method trying to do a clever find of workspaces...

We should probably think of another way to make this convenient... ( configuration vs autodetection ?)

[asmodehn]

It seems _setup_utils.py doesnt do anything regarding the setup of the environment. Instead it helps generate shell scripts... so maybe we cant use it after all ?

[asmodehn]

On the other hand the output of _setup_util is quite simple and we might be able to parse it ?