GEOMESA-151 allowing schema to not be set in datastore config for already created features

Since geoserver doesn't even have the ability right now to configure a custom schema.
Hrrm... this is a hair-splitting issue.  I can appreciate building up the errors.  In terms of idiomatic Scala, I'd suggest refactoring this method and it's calling method so that we iterate over a collection of 'checks' which produce Option[String] error messages.  (The iteration can be flatMap, and we'll have a sequence/list of the errors.)

Anyhow, I can't quite sort out a great solution with Try/Either.