engine_page: Display correctly proto for Manage by

On status page, we have the "Manage by" string to
show to users which oVirt Engine the node is registered.
This patch will add a validation which protocol it used during
the registration (http or https) and put it in the display.

Change-Id: Iecfc53bab7e5f6ab226ded7f00bd6d140b6846b1
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1065401
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>