Increase the ESP partition size to 550 MB

This change makes ironic-lib consistent with ironic-python-agent
and diskimage-builder's defaults for ESP partition sizes.

The following fedora change lays out why this is a necessary
change: https://fedoraproject.org/wiki/Changes/BiggerESP

In summary, additional space is needed if OS driven firmware
flashing is going to take place, and unikernels + next generation
bootloaders are going to consume more space than the existing
grub loader has.

Change-Id: I4fc63c02bf57a08e75121cfa1fd35a56c0427553

ironic_lib/disk_utils.py

@@ -35,9 +35,12 @@ from ironic_lib import utils
 
 opts = [
     cfg.IntOpt('efi_system_partition_size',
-               default=200,
+               default=550,
                help='Size of EFI system partition in MiB when configuring '
-                    'UEFI systems for local boot.'),
+                    'UEFI systems for local boot. A common minimum is ~200 '
+                    'megabytes, however OS driven firmware updates and '
+                    'unikernel usage generally requires more space on the '
+                    'efi partition.'),
     cfg.IntOpt('bios_boot_partition_size',
                default=1,
                help='Size of BIOS Boot partition in MiB when configuring '

releasenotes/notes/increase-efi-partition-size-9479d069b17804ce.yaml

@@ -0,0 +1,12 @@
+---
+other:
+  - |
+    The default size of EFI system partitions to be created, when writing a
+    partition image, has been increased to 550 Megabytes from 200 Megabytes.
+    If this change is undesirable, please utilize the
+    ``efi_system_partition_size`` configuration option. This value is now
+    also consistent with the internal default when creating ESP volumes
+    for Software RAID with ``ironic-python-agent``, and the default carried
+    by ``diskimage-builder``. The prime driver for an increased partition
+    size is to enable OS driven firmware updates and appropriate space to
+    house Unikernels which requires additional space.