Allow defining custom script when running init_multicloud (via @custo…

…m_script_pre@: before a kube DNS is set and @custom_script_post@: after a kube DNS is set)

(cherry picked from commit 8801ed4)

scripts/autoscaling/init_multicloud_v1.15.4.sh

@@ -174,7 +174,7 @@ wget $_WO "${GLOBAL_DISTRIBUTION_URL}tools/nvme-cli/1.16/nvme.gz" -O /bin/nvme.g
 gzip -d /bin/nvme.gz && \
 chmod +x /bin/nvme
 
-@custom_script@
+@custom_script_pre@
 
 swap_size="@swap_size@"
 setup_swap_device "${swap_size:-0}"
@@ -481,6 +481,8 @@ systemctl start kubelet
 
 update_nameserver "$nameserver_post_val" "infinity"
 
+@custom_script_post@
+
 if [[ $FS_TYPE == "btrfs" ]]; then
   _MOUNT_POINT="/ebs"
   _FS_AUTOSCALE_PRESENT=0