Change port used for Ironic static http to 3928

Due to recent infrastructure changes, infra began using port 8088. This
caused a conflict with our apache config, causing services to not start.
Infra is changing this port (Ie67bbba02dbf61a481f66001de3e0dede9448316)
but it may take up to a week to take effect.

Instead of having our gate broken for a week, I'm changing the default
port. 3928 was not chosen at random; it's listed as the netboot-pxe
service port in /etc/services.

Change-Id: Ifdcf3c82fd9ee64c1548e47dba4c78c2347959e0
Co-Authored-By: John L. Villalovos <john.l.villalovos@intel.com>
Closes-bug: 1590139
(cherry picked from commit 2898b62)

devstack/lib/ironic

@@ -142,7 +142,7 @@ IRONIC_HOSTPORT=${IRONIC_HOSTPORT:-$SERVICE_HOST:$IRONIC_SERVICE_PORT}
 IRONIC_IPXE_ENABLED=$(trueorfalse False IRONIC_IPXE_ENABLED)
 IRONIC_HTTP_DIR=${IRONIC_HTTP_DIR:-$IRONIC_DATA_DIR/httpboot}
 IRONIC_HTTP_SERVER=${IRONIC_HTTP_SERVER:-$HOST_IP}
-IRONIC_HTTP_PORT=${IRONIC_HTTP_PORT:-8088}
+IRONIC_HTTP_PORT=${IRONIC_HTTP_PORT:-3928}
 
 # Whether DevStack will be setup for bare metal or VMs
 IRONIC_IS_HARDWARE=$(trueorfalse False IRONIC_IS_HARDWARE)