Make it possible to call another grml command

[skaldesh]

I have the use case right now that I would like to execute another grml command (e.g. grml.train.clear), if in my current command (e.g. grml.train) a certain condition is true. So I want to run that conditionally.

Maybe it would be cool, if we could write:

exec: |
   ...
   if [ some-condition ]; then
      grml.train.clear
   fi

[skaldesh]

This is already possible with grml -D ${ROOT} cmd