Add default master_hostname

Change-Id: I52dc5de96c2754ce52b1d26f6daa81509ef671d6
diff --git a/bootstrap.sh b/bootstrap.sh
index c589d6a..0cac518 100755
--- a/bootstrap.sh
+++ b/bootstrap.sh
@@ -75,6 +75,7 @@
 # salt
 export SALT_MASTER=${SALT_MASTER:-127.0.0.1} # ip or fqdn
 export MINION_ID=${MINION_ID:-${HOSTNAME}.${DOMAIN}}
+export MASTER_HOSTNAME=${MASTER_HOSTNAME:-${HOSTNAME}.${DOMAIN}}
 
 # saltstack
 BOOTSTRAP_SALTSTACK=${BOOTSTRAP_SALTSTACK:-True}