Generalize passing Java properties

[ip1981]

Generalize passing Java properties, e. g. for Jenkins or Cassandra.

Whatever in jre.properties should be automatically and correctly passed to JRE. For example see MariaDB or PostgreSQL:

jre = {
      package = mkOption {
        description = "Java runtime package";
        default = pkgs.jre8;
        type = package;
      };

      properties = {
        cassandra.config = readonly "file://${configFile}" str;
        java.io.tmpdir = readonly "${config.home}/tmp" path;
        java.library.path = default [ "${config.package}/lib/jni" ] (listOf path);
        foo.whatever = default {} (attrsOf str);
      };
};