Do not add CNAME grunt warning for manual deployment type

This prevents `grunt.warning` for missing CNAME if `options.deployType` is set to `manual`. 

As `manual` is only uploading a new version to the application there is no need to provide a CNAME.
@ecaron I thought I'd do it this way so the log messages are consistent regardless of which deploy type you choose. It does add a little overhead running what is essentially a useless test so maybe it's best to skip the check entirely as suggested. What do you think?