TT#51600 Use hostname from ip= if install from puppet

HOSTNAME env variable is not set from 'ip=' but seems to be set
outside of deployment.sh script and exported to it. HOSTNAME
variable is set differently if newer grml20181230 is set in
dnsmasq dhcp.conf. We have 'ip=' option where we explicitly set
hostname for the host so let's use it (instead of uncontrolled
HOSTNAME variable) for puppet installation case.

Change-Id: I3fa2cc7ec982b270302d2d0940d6477b666eaf5c

templates/scripts/includes/deployment.sh

@@ -2091,9 +2091,9 @@ puppet_install_from_puppet () {
 
   set_deploy_status "puppet"
 
-  echo "Setting hostname to $TARGET_HOSTNAME"
-  echo "$TARGET_HOSTNAME" > ${TARGET}/etc/hostname
-  grml-chroot $TARGET hostname -F /etc/hostname
+  echo "Setting hostname to ${IP_ARR[hostname]}"
+  echo "${IP_ARR[hostname]}" > "${TARGET}/etc/hostname"
+  grml-chroot "$TARGET" hostname -F /etc/hostname
 
   chroot $TARGET apt-get -y install resolvconf libnss-myhostname