Bug 1119240 - Adding http-interface in the host controller's host-slave.xml
is not recognised by JBoss ON Agent causing Host Controller's availability
to stay DOWN

throw InvalidPluginConfiguration exception when http mgmt interface port is
detected as 0 (not-detected). User is advised to set his host controller up
and then update connection settings.

(cherry picked from commit 2d3a7af207833a95e619422e3b788cb30e7ffb69)
Signed-off-by: Libor Zoubek <lzoubek@redhat.com>