Update some message formats

Use PID_FMT/USEC_FMT/... in more places.

Also update logind error messages to print the full path to a file that
failed. This should make debugging easier for people who do not know
off the top of their head where logind stores it state.
udev: add zram to the list of devices inappropriate for symlinks

udev seems to have a race condition with swapon to see which can open
/dev/zram0 first, causing swapon to fail. Seems to be most noticeable
on arm devices one out of every 7 times or something.