CI: adjust .ci/common.py users to pmbootstrap ci (MR 3608)

Adjust all CI scripts that make use of .ci/common.py to
'pmbootstrap ci'. Move all scripts that are not direct entry points to
running CI scripts to .ci/lib.

Comment out the dtb check, as it is failing. Apparently it didn't run
properly before. Let's fix this after this CI change is done.