atlasboard generate dashboard generates files in a sub-folder

[Ben Wong]

atlasboard generate dashboard creates dashboard.json in a sub-folder under the dashboards folder. These files should be created directly in the dashboards folder instead.

[Iván Loire]

Fixed for 2.0.1. I also added some additional test coverage.

https://bitbucket.org/atlassian/atlasboard/commits/01223e4f4709bea2435e0ac177a4e8722b3a5f36