Fix creation of ram device on Alinux2

Before creating the ram device, be sure that the brd (block ram disk) module is loaded,
otherwise you'll get the error:
```
Could not stat /dev/ram1 --- No such file or directory

The device apparently does not exist; did you specify it correctly?
```

Fix aws/aws-parallelcluster#2407

Signed-off-by: Luca Carrogu <[email protected]>

Author: lukeseawalker

CHANGELOG.md

@@ -14,6 +14,7 @@ This file is used to list changes made in each version of the AWS ParallelCluste
 
 **BUG FIXES**
 - Use non interactive `apt update` command when building custom Ubuntu AMIs.
+- Fix `encrypted_ephemeral = true` when using Alinux2
 
 2.10.1
 ------

files/default/setup-ephemeral-drives.sh

@@ -81,6 +81,7 @@ function setup_ephemeral_drives () {
     vgcreate vg.01 $PARTITIONS || RC=1
     lvcreate -i $NUM_DEVS -I 64 -l 100%FREE -n lv_ephemeral vg.01 || RC=1
     if [ "$cfn_encrypted_ephemeral" == "true" ]; then
+      modprobe brd || RC=1
       mkfs -q /dev/ram1 1024 || RC=1
       mkdir -p /root/keystore || RC=1
       mount /dev/ram1 /root/keystore || RC=1