Install plugin should generate md5 in same format as md5sum

maven-install-plugin generates md5 and sha1 files that contain just a checksum (and no newline), whereas md5sum generates a file with a checksum and the file name.

It would be good to support that format.

See discussion in CALCITE-747. I would rather use maven than resorting to shell scripts as the Phoenix project has (see a later comment in that thread).