Include patch/* and dropin/* on brooklyn class path

- brooklyn distribution contains empty ./patch and ./dropin dirs
- brooklyn class path includes patch/* (before lib) and
  dropin/* (after lib) on the class path.

Aim is to make it even easier to add additional entities etc, without 
messing with lib directory or having to set BROOKLYN_CLASSPATH.
Merge pull request #935 from aledsage/feature/dist-dropin-folder

Include patch/* and dropin/* on brooklyn class path