New FSx DNS name does not automatically update in /etc/fstab

**Environment:**
- AWS ParallelCluster / CfnCluster version [aws-parallelcluster-2.6.1]
- Configuration file (i.e. ~/.parallelcluster/config) without any credentials or personal data.

```
[aws]
aws_region_name = us-east-1

[global]
cluster_template = default
update_check = true
sanity_check = true

[aliases]
ssh = ssh {CFN_USER}@{MASTER_IP} {ARGS}

[cluster default]
key_name = xxx
base_os = ubuntu1804
scheduler = slurm
max_queue_size = 20
maintain_initial_size = true
vpc_settings = slurm
compute_instance_type = c4.8xlarge
master_instance_type = r5a.4xlarge
#extra_json = {"cluster": {"ganglia_enabled": "yes"}}
fsx_settings = slurmfsx
initial_queue_size = 0
scaling_settings = slurm

[fsx slurmfsx]
# comment out shared_dir and storage_capacity when adding fsx id
shared_dir = /fsx
storage_capacity = 1200
#fsx_fs_id =

[vpc slurm]
vpc_id = vpc-xxx
master_subnet_id = subnet-xxx
compute_subnet_id = subnet-xxx
use_public_ips = false

[scaling slurm]
scaledown_idletime = 15
```

**Bug description and how to reproduce:**
The FSx Lustre file system mount point is automatically added to `/etc/fstab` during initial cluster launch.

When making a change to an FSx Lustre file system that results in a replacement (e.g. altering the `deployment_type`), the file system itself properly deletes and redeploys, but the FSx mount point does not properly update in `/etc/fstab` on the cluster nodes.

In this example, the previous FSx file system ID was `fs-0c72f1afba7504877`, but the newly created one was obviously different (`fs-054a3ce927a2ac593`)

```
ubuntu@ip-10-0-30-157:~$ cat /etc/fstab
LABEL=cloudimg-rootfs / ext4 defaults,discard 0 0
UUID=8ec824a0-5eec-42a0-80be-9ecd13d6f38d /shared ext4 _netdev 0 0
fs-0c72f1afba7504877.fsx.us-east-1.amazonaws.com@tcp:/fsx /fsx lustre defaults,_netdev,flock,user_xattr,noatime,noauto,x-systemd.automount 0 0
```


I was not able to test if new compute nodes scale in with the correct file system ID, but I did confirm that existing nodes did not get updated when the FSx file system redeployed.

Let me know if there's any other information or test cases I can provide, thanks!