Add explanation to errors `spec_build_failed` and `format_build_failed` on https://ci.kaitai.io/

[Mingun]

I think, it is possible to get the concrete error, similar to failed status and show it in the test matrix. For now, I have no idea what they means?

[Mingun]

I found, that format_build_failed and spec_build_failed means the same, but the second is used when corresponding KST configuration test receipt is found in spec/ks.

Both statuses means that code from KSY was generated, but failed to compile / run (I checked Java runner). It seems redundant. I think, the following 4 statuses should be used:	Status	Meaning
generation_error	KSC failed to generate files from KSY
build_error	KSC successfully generated files, but their are fail to compile / run
failed	Build is successful, but test assertion fail
passed	Build is successful and test is green

Files for tests comes from

• https://github.com/kaitai-io/kaitai_struct_formats/
• formats folder