dib-lint: validate json/yaml files
dib-lint: validate json/yaml files

Look for files .yaml and pkg-map configurations, and try to load them
either as json or yaml. This way, invalid ones can be detected before
they are committed unnoticed.

Also, exclude .yaml files from being searched while checking bash and
python scripts.

Change-Id: I2478837cfe66929ae1b0d7dd96e049773a35e11c

zioproto/diskimage-builder,switch-ch/diskimage-builder,takahashinobuyuki/diskimage-builder,switch-ch/diskimage-builder,takahashinobuyuki/diskimage-builder,zioproto/diskimage-builder,CSC-IT-Center-for-Science/diskimage-builder,CSC-IT-Center-for-Science/diskimage-builder,openstack/diskimage-builder,openstack/diskimage-builder