Make deleteDatabase test in Nightwatch more specific

Correct me if I'm wrong, but I'm not sure this makes sense. The database name isn't wrapped in double quotes in the page - only the URL, correct? So this will never match + thus always pass. 

How about renaming the createdDatabaseIsNotPresent to createdDatabaseIsPresent and test for its negation:

```javascript
        var data = result.value, 
            createdDatabaseIsPresent = data.indexOf('"/#/database/' + newDatabaseName + '/_all_docs"');

        this.verify.ok(createdDatabaseIsPresent === -1,
          'Checking if new database no longer shows up in _all_dbs.');
```