run from ORIENTDB_HOME, set CLASSPATH properly, log config assumes same

This revision to server.sh trusts the user's setting for $ORIENTDB_HOME to be correct (i.e. doesn't check for bin/orient.sh, bin/server.sh, etc.).  The server will fail quickly enough if it's wrong.  If not provided, $ORIENTDB_HOME defaults to "`dirname $0`/..".  The script changes dir to $ORIENTDB_HOME before running JVM. This required a change to the path for the log file in the orientdb-server-log.properties. This results in a more understandable path: "log/" rather than "../log", which required the user to understand the script switched to bin before running.