Set config param [DEFAULT]/host to hostname

Patch: https://review.openstack.org/#/c/352806 has
set host=None and we don't change this parameter
neither in devstack installation nor in manual installation.
With this patch value of [DEFAULT]/host is set to
hostname of the host on which magnum is setup.
Also, updated manual installation step to set [DEFAULT]/host
to hostname.

Depends-on: I51feb6ccdc0fab91a591568866e6801f2bbb319b
Change-Id: Id43bfcc792b28c98c9bf1d888dd7ddcc167e8ea5
Closes-Bug: #1630190

devstack/lib/magnum

@@ -126,9 +126,11 @@ function create_magnum_conf {
 
     # (Re)create ``magnum.conf``
     rm -f $MAGNUM_CONF
+    HOSTNAME=`hostname`
     iniset $MAGNUM_CONF DEFAULT debug "$ENABLE_DEBUG_LOG_LEVEL"
     iniset $MAGNUM_CONF DEFAULT transport_url \
           "rabbit://$RABBIT_USERID:$RABBIT_PASSWORD@$RABBIT_HOST"
+    iniset $MAGNUM_CONF DEFAULT host "$HOSTNAME"
 
     iniset $MAGNUM_CONF database connection `database_connection_url magnum`
     iniset $MAGNUM_CONF api host "$MAGNUM_SERVICE_HOST"