Add a separate /boot partition

The overcloud-hardened-uefi-full image now has a separate partition
mounted to /boot. This means grub no longer needs to mount the root
partition. This will allow trying layouts which grub doesn't support,
such as LVM thin-provisioning. Since grub now uses the common path of
loading an ext4 /boot partition, early boot may now be more robust, or
have better error messages for incorrectly built images.

Change-Id: I27be9c3e82ed20dcfc7a6f7dcb992006d44f933f
(cherry picked from commit e57e998b0e)

elements/overcloud-partition-uefi/block-device-default.yaml

@@ -17,9 +17,19 @@
       - name: BSP
         type: 'EF02'
         size: 8MiB
+      - name: boot
+        type: 'BC13C2FF-59E6-4262-A352-B275FD6F7172'
+        size: 500MB
+        mkfs:
+          type: ext4
+          mount:
+            mount_point: /boot
+            fstab:
+              options: "defaults"
+              fsck-passno: 1
       - name: root
         flags: [ boot ]
-        size: 6G
+        size: 5500MB
 - lvm:
     name: lvm
     base: [ root ]

releasenotes/notes/boot-partition-6ad1ce7255b1715e.yaml

@@ -0,0 +1,9 @@
+---
+features:
+  - |
+    The overcloud-hardened-uefi-full image now has a separate partition mounted
+    to /boot. This means grub no longer needs to mount the root partition. This
+    will allow trying layouts which grub doesn't support, such as LVM
+    thin-provisioning. Since grub now uses the common path of loading an ext4
+    /boot partition, early boot may now be more robust, or have better error
+    messages for incorrectly built images.