java_export should not generate publisher script with credentials in it

[dr-dime]

credentials should be kept in

• files that are read-only to the current user or
• in memory.

The current design of _maven_publish_impl will generate a file with credentials in it and the file will be uploaded to the remote cache, thus made available for anyone who has access to it.

All these credentials should be passed at the run time of the script, not the build time, ie. bazel run pkg.publish -- --user=x --password=y and more preferably from a maven config file, eg. .m2/settings.xml.

Relevant topics:

• bazelbuild/bazel#498
• #80