Gerrit should include the common role as a dependency I think, unless there is something in the common role that you don't think we need for it. 

Create `gerrit/meta/main.yml` with the following contents:

```
---
dependencies:
  - common
```

then, you might set the following default directories:
```
gerrit_app_dir: "{{ COMMON_APP_DIR }}/gerrit"
gerrit_data_dir: "{{ COMMON_DATA_DIR }}/gerrit"
```