We validate the boot interface during adoption because of:
a) potential rebuilding,
b) non-local boot.
Rebuild proved a rarely used feature, and local boot is the default
nowadays, so it makes less sense to unconditionally validate the boot
interface during adoption. We will run the validation anyway the next
time we need to do something with booting.
Similarly, do not record is_whole_disk_image None if it cannot be
reliably determined.
Change-Id: I95252aea808c48ea2d94569449c871f0d483caaa
d342b07dd6