Handle OpenJDK "jmod" files

This bug was originally reported by Emmanuel Bourg (ebourg@apache.org) in Debian bug #933337:

Starting with the version 9 and the new module system OpenJDK has .jmod files
containing compiled classes and resources. This container format is basically
a ZIP file prefixed with 4 bytes: "4A 4D 01 00".

Could you please handle these files in strip-nondeterminism, clamping the
timestamps and sorting the entries?

jmod files can be found in the openjdk-11-jdk package, in the
/usr/lib/jvm/java-11-openjdk-amd64/jmods/ directory.