In donut, OTA installation often encounters the write() system call
doing short writes -- which is legal but unexpected -- or failing with
ENOSPC when plenty of space is available. Passing aligned memory
buffers to write() appears to prevent (or at least reduce the
frequency) of these problems. b/1833052 has been filed to look at the
underlying problem, but this change aligns buffers we use with write()
so we can OTA for now (or see if this problem still occurs).
minzip fails if write() doesn't write all the data in one call.
Apparently this was good enough before, but it causes OTAs to fail all
the time now (maybe due to the recently-submitted kernel)? Change
code to attempt continuing after short writes.
