log4j properties config revamp

180356d9a264f103ed661b31ad0625a6c10873dd introduces Log4j config separate files for gremlin.sh and gremlin-server.sh:

* gremlin.sh: gremlin-groovy/src/main/config/log4j-repl.properties
* gremlin-server.sh: gremlin-server/config/log4j-server.properties

Test JVMs forked by Surefire and Failsafe use the server config file by default.  The file is controlled by a pair of properties defined in the top-level pom:

* `${log4j.properties}`
* `${log4j.properties.dir}`

This commit also rewrites gremlin.sh.  It now accepts a `-l <LOGLEVEL>` option.  I only tested -l TRACE, -l DEBUG, and -l WARN, but each appeared to work as advertised (I executed `bin/gremlin.sh` after running `mvn clean install`).

I didn't rewrite gremlin-server.sh.  I just made minimal changes to point it at log4j-server.properties at the path mentioned above.  It does not accept a `-l <LOGLEVEL>` option, but it could with some additional editing.

`bin/gremlin.sh -v` does not work.  This is a preexisting problem.  The class `com.tinkerpop.gremlin.Version` doesn't exist and running `find -name 'Version*'` yielded nothing, so I left that broken.