Simplify generation of VersionInfoMain and Info

The VerGen command is currently compiled and executed in a separate step prior to compilation of the rest of zookeeper-server. This is wasteful, complicated, and unnecessary.

Maven has built-in resource filtering for classes, so you can inject the system properties into the build and generate sources to be compiled that have the necessary information. (For example, see Accumulo's FilteredConstants).

I have a pull request ready to address this, which I will push up shortly.