Explicitly set boot_mode to legacy BIOS

Since we currently only support legacy BIOS boot mode, set it explicitly
in node capabilities. This is especially important since Ironic changed
the default boot mode to UEFI in Yoga. If the capabilities field is
provided, the boot_mode should be set explicitly.

This change should be followed by one that adds support for UEFI boot
mode.

Change-Id: I0c1e0cc50119cc2f9ba3e0b0a3548baeca9dca2e

Author: markgoddard

ansible/roles/ironic-enrolment/tasks/node.yml

@@ -102,6 +102,11 @@
           cpus: "{{ node.vcpus }}"
           memory_mb: "{{ node.memory_mb }}"
           local_gb: "{{ node.volumes[0].capacity | size_string_to_gb if node.volumes | length > 0 else 0 }}"
+          # Since we currently only support legacy BIOS boot mode, set it
+          # explicitly here. This is especially important since Ironic changed
+          # the default boot mode to UEFI in Yoga. If the capabilities field is
+          # provided, the boot_mode should be set explicitly.
+          capabilities: "boot_mode:bios"
 
     - name: Add Ironic node traits
       command: >-