Attributes with an empty string are not nil...
This fixes a small issue we discovered, since we lay down the certificates with another recipes, we just point gitlab-omnibus at the specific files. changes in the default recipe made it so it overwrote the files that were already in place. since the attributes have '' as defaults in the ssl hashes when the default recipe checked for nil? it would return try and then set the content of the file to empty. the empty? call works better for the attribute defaults.
