Since I4f2cecdc0af366364b18232dbd8ea4ffdd3165d2, bootloader installation
failures were ignored to facilitate backwards compatibility with older
Ironic Python Agents. However, this means that some genuine failures are
ignored.
We can now rely on having a sufficiently modern IPA, so this patch makes
bootloader installation failures fatal for whole disk images.
Change-Id: Ic280cc3e1a2bb462d5425efd71b336db8c14bb90
ca6499b62c