init: Actually check the return value for calls during first stage init

Init never checked the return values of the calls made during first
stage init (since of course they're not going to fail, right?).  But
of course commands can fail and they might not necessarily be obvious
when they do, so let's make it obvious.

Since the kernel log isn't up until later, this creates a list of the
failures that can then be sent to the kernel log once it's ready
(pending of course failures in setting it up...)

Test: boot bullhead, don't see errors
Change-Id: I8c12c61fa12e4368346e8b0e1c0bb0844b5d0377