bundle search seem to include bundles that are present in ROCK_BUNDLE_PATH

[doudou]

Problem reported by @maltewl in rock-core/package_set#16

I had two problems (possibly related):

  1) Errors from another bundle leak into the current one. E.g. put some random text into models/actions/main.rb of bundle 'B'. It will break a `syskit instanciate` command in another bundle ('A') which has no dependency on bundle 'B'.

  2) Searching for files behaves not as expected. I would expect that `Roby.app.find_files_in_dirs` is limited to the loaded bundles, but is searches within all folders defined in `ROCK_BUNDLE_PATH`.

Possibly, the problem occurs when a bundle is explicitly listed in ROCK_BUNDLE_PATH