cmgr error reporting should be more verbose

[dbrumley]

cmgr should tell you what it was trying to do, and on which problem, when it encounters an error.

Case in point: I have 46 challenges in a schema file, and I get this error but have no idea which challenge is causing it:

error: failed to build image: The command '/bin/sh -c make && echo "picoCTF{$FLAG}" > flag.txt' returned a non-zero code: 2

I went through the docs and found export CMGR_LOGGING=debug, which helps here, but it's annoying that I had to do these extra steps.

[dmartin]

Agreed, templating challenge IDs and additional metadata directly into error messages would be a good improvement to reduce the necessity for debug logging.