java_gen: dedicated factories for (action|instruction)_id, erromsg

also moved the errormsg subclasses to their own package (errormsg)
bumped openflowj version to 0.3.2
Merge into master from pull request #154:
java_gen: dedicated factories for (action|instruction)_id, erromsg (https://github.com/floodlight/loxigen/pull/154)