Defining multiple classes inside an easyblock file

[Crivella]

As of know, defining multiple classes inside an easyblock file will cause eb --list-easyblocks and its associated unittest to fail (see https://github.com/easybuilders/easybuild-easyblocks/pull/3338 for example)

Considering all formal easyblocks class names are supposed to start with EB_ i was wondering if it could make sense to change the regex at https://github.com/easybuilders/easybuild-framework/blob/ae2958838bfde991424a687782a78fa7f7703775/easybuild/framework/easyconfig/tools.py#L753 to search only for classes starting with EB_.