Compressed images are not a multiple of device block size

[jgallagher]

I created a recovery image, which is compressed; its size is not a multiple of 4096 (or even 512):

john@helios1:~/helios/image/output$ ls -l
total 906133
-rwxr-xr-x   1 john     staff    25165824 May 11 23:33 cpio
-rw-r--r--   1 john     staff    8488461 May 11 23:33 cpio.z
-rw-r--r--   1 john     staff    223346400 May 11 23:33 os.tar.gz
-rw-r--r--   1 john     staff    33554432 May 11 23:33 rom
-rw-r--r--   1 john     staff     770069 May 11 23:33 unix.z
-rw-r--r--   1 john     staff    208880346 May 11 23:33 zfs.img

Normally recovery images are streamed in over the uart, so this is fine, but I wanted to write this directly to an M.2 to get faster debug laps. Manually padding zfs.img with zeroes out to a multiple of 4096 allowed it to work with pilot bsu, but could this tool do that itself instead?