Partition images can sometimes contain a /boot folder structure
event he assets for EFI booting on that filesystem. Which is a
good thing. The conundrum is that Ironic does not handle this
properly and potentially replaces the bootloader in this sequence
such that grub2-install is used instead of signed bootloader assets.
As such, we should be preserving the assets and using them from
a partition image much like we do when we have a wholedisk
image and can identify the assets.
Now we will preserve the EFI boot assets, copy them to the new EFI
boot partition, and call the EFI setup methods to manage the EFI
nvram.
Note, this change also splits the logic path out that performs the
end call of the EFI boot manager into a reusable method but does
not retool all of the testing as it is intertwined in the
install_grub2 testing.
Also adds some additional debug logging, as much of the bootloader
installation code has multiple fallback/cleanup points which makes
it difficult to debug from logs.
Story: 2008070
Task: 40753
Change-Id: If17d4b4c06df5504987e61a1fde6662e9acd6989
f9870d5812