Add more logging to "Guest user can set display names" (#846)

tests/30rooms/13guestaccess.pl

@@ -172,13 +172,19 @@
                displayname => "creeper",
             },
       )})->then( sub {
+         my $iter = 0;
+
          retry_until_success {
+            $iter++;
+
             Future->needs_all(
                do_request_json_for( $guest_user,
                   method => "GET",
                   uri    => $displayname_uri,
                )->then( sub {
                   my ( $body ) = @_;
+                  log_if_fail "Iteration $iter: /displayname result", $body;
+
                   assert_eq( $body->{displayname}, "creeper", "Profile displayname" );
 
                   Future->done(1);
@@ -188,6 +194,8 @@
                   uri    => "/r0/rooms/$room_id/state/m.room.member/:user_id",
                )->then( sub {
                   my ( $body ) = @_;
+                  log_if_fail "Iteration $iter: /state result", $body;
+
                   assert_eq( $body->{displayname}, "creeper", "Room displayname" );
 
                   Future->done(1);