frontend: fix broken layout in new/edit vm -> console tab

This regression has been introduced by
09d246450ad7b7fbda1dcf54c806fdb8d181a201

This patch adds the possibility to turn off the feature
introduced in the mentioned patch.

Change-Id: If4f8ec3b9426059803a3331c47bffc7cad9ac6c5
Signed-off-by: Tomas Jelinek <tjelinek@redhat.com>