TEST-46-HOMED: check for support on /dev/shm and /tmp separately

TEST-46-HOMED: check for support on /dev/shm and /tmp separately

The test fails in CI. My guess was this is because the enablement of quota on
/tmp and /dev/shm is independent. The former fs is mounted by systemd in the
host, while the latter is mounted in the initrd, so we can end up with quota
support on one but not the other, which is the situation I had on my laptop.
This wasn't actually the source of the problems in CI, but it's a reasonable
change to make anyway.

While at it, test both mountpoints separately.