Merge pull request #544 from DataDog/albertvaka/check-match-group-exists-1

Raise if hostname_extraction_regex doesn't capture hostname

Author: albertvaka

lib/puppet/reports/datadog_reports.rb

@@ -22,6 +22,9 @@
     rescue
       raise(Puppet::ParseError, "Invalid hostname_extraction_regex #{HOSTNAME_REGEX}")
     end
+    unless HOSTNAME_EXTRACTION_REGEX.named_captures.has_key? "hostname"
+      raise(Puppet::ParseError, "hostname_extraction_regex doesn't include a match group named 'hostname': #{HOSTNAME_REGEX}")
+    end
   else
     HOSTNAME_EXTRACTION_REGEX = nil
   end