Here's reason.

in a package distribution, drivers should be packaged like

```
${ZEPPELIN_HOME}/drivers/hive11
                        /exec
                        /presto
```

To make this happen, each driver's maven-dependency-plugin copies it's dependency and artifact to under /drivers/subdir/
Also, advantage of this location is, we can still run zeppelin-server using eclipse when in development. zeppelin-server will looking for driver directory to load drivers.

Driver jar and it's dependency should not be in class path of zeppelin-server (should not be in lib dir). because we want load them in separate class loader.