This is another part of the breakup of the massive BuildPlugin. This PR
moves the code for configuring publications to a separate plugin. Most
of the time these publications are jar files, but this also supports the
zip publication we have for integ tests.
BuildPlugin is a catch all for any elasticsearch common build
infrastructure. Unfortunately that makes reusing parts of it difficult.
This commit splits the parts specific to all java based projects out to
our own elasticsearch.java plugin.
