Add sails root path to sails-generate, fixes #1725

https://github.com/balderdashy/sails/issues/1725
```sails new appname``` works, however ```sails generate new appname```  throws:
```
fs.js:718
  binding.symlink(preprocessSymlinkDestination(destination, type),
          ^
TypeError: dest path must be a string
``` 
It happens because sails root path is not set in sails-generate.