Fix teardown issue

Hi, I ran into an issue with the teardown while writing some tests with mocha.
Lowering sails does not teardown the database correctly so on subsequent lifts I get this error
```
A hook (`orm`) failed to load!
AdapterError: Connection is already registered
```
After some googling I found [sails-memory](https://github.com/balderdashy/sails-memory) and [sails-postgresql](https://github.com/balderdashy/sails-postgresql) had the same issue.
These issues were discussed in balderdashy/sails#1632 and  balderdashy/sails#2332. 

I tried the solution presented in balderdashy/sails-memory@545f61acb3cfe3eca01c44370414e36ce0a067e3 and balderdashy/sails-postgresql#127 and it seems to work fine.