Use strongloop test MySQL server for testing

/to @bajtos or @ritch 

The PR allows we to use https://github.com/strongloop/strongloop-config for testing mysql.
When this condition fails, the error message will be very unhelpful, as it won't print the actual error code.

A better solution:

```
expect(pingError.code).to.match(/^ECONNREFUSED|ER_ACCESS_DENIED_ERROR/);
```

However, I find it very suspicious that you consider the test `it('returns descriptive error for invalid credentials)` as passed when the credentials were not checked at all.