un-rename cct key for checksum
un-rename cct key for checksum

We changed dogen to use md5sum: as the key value for md5sums, but
we haven't (yet) changed cct. Therefore, adjust cct module to continue
to look for the (old/existing) key value 'chksum'.

goldmann/dogen,jboss-container-images/concreate,jboss-dockerfiles/dogen,jboss-container-images/concreate,goldmann/dogen,jboss-dockerfiles/dogen,goldmann/dogen,jboss-container-images/concreate,jboss-dockerfiles/dogen