engine_page: Replace oVirt Engine str with constant

Use constant for product name instead of static value.

Change-Id: I989fec8c90c27bad4e8a3dca810ab492253929dd
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1167246
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>