def normalize_set_identifier(identifier)
      case identifier
      when nil, ""
        @environment_name
      when :all, "all"
        nil
      when Array
        identifier.map { |i| normalize_set_identifier(i) }.uniq.join(",")
      else
        identifier.to_s
      end
    end
def normalize_set_identifier(identifier)
      case identifier
      when nil, ""
        @environment_name
      when :all, "all"
        nil
      when Array
        identifier.map { |i| normalize_set_identifier(i) }.uniq.join(",")
      else
        identifier.to_s
      end
    end
Converts the given identifier to a rvm-friendly form.
 Unlike using sets directly, a nil identifier is set
 to mean the current ruby (not all). :all or "all" will
 instead return the a blank identifier / run it against
 all rubies.