fstests: add helper to canonicalize devices used to enable persistent disks

fstests: add helper to canonicalize devices used to enable persistent disks

The filesystem configuration file does not allow you to use symlinks to
real devices given the existing sanity checks verify that the target end
device matches the source. Device mapper links work but not symlinks for
real drives do not.

Using a symlink is desirable if you want to enable persistent tests
across reboots. For example you may want to use /dev/disk/by-id/nvme-eui.*
so to ensure that the same drives are used even after reboot. This
is very useful if you are testing for example with a virtualized
environment and are using PCIe passthrough with other qemu NVMe drives
with one or many NVMe drives.

To enable support just add a helper to canonicalize devices prior to
running the tests.

This allows one test runner, kdevops, which I just extended with
support to use real NVMe drives it has support now to use nvme EUI
symlinks and fallbacks to nvme model + serial symlinks as not all
NVMe drives support EUIs. The drives it uses for the filesystem
configuration optionally is with NVMe eui symlinks so to allow
the same drives to be used over reboots.

For instance this works today with real nvme drives:

mkfs.xfs -f /dev/nvme0n1
mount /dev/nvme0n1 /mnt
TEST_DIR=/mnt TEST_DEV=/dev/nvme0n1 FSTYP=xfs ./check generic/110

FSTYP         -- xfs (debug)
PLATFORM      -- Linux/x86_64 flax-mtr01 6.5.0-rc3-djwx #rc3 SMP PREEMPT_DYNAMIC Wed Jul 26 14:26:48 PDT 2023

generic/110        2s
Ran: generic/110
Passed all 1 tests

But this does not:

TEST_DIR=/mnt TEST_DEV=/dev/disk/by-id/nvme-eui.0035385411904c1e FSTYP=xfs ./check generic/110
mount: /mnt: /dev/disk/by-id/nvme-eui.0035385411904c1e already mounted on /mnt.
common/rc: retrying test device mount with external set
mount: /mnt: /dev/disk/by-id/nvme-eui.0035385411904c1e already mounted on /mnt.
common/rc: could not mount /dev/disk/by-id/nvme-eui.0035385411904c1e on /mnt

umount /mnt
TEST_DIR=/mnt TEST_DEV=/dev/disk/by-id/nvme-eui.0035385411904c1e FSTYP=xfs ./check generic/110
TEST_DEV=/dev/disk/by-id/nvme-eui.0035385411904c1e is mounted but not on TEST_DIR=/mnt - aborting
Already mounted result:
/dev/disk/by-id/nvme-eui.0035385411904c1e /mnt

This fixes this. This allows the same real drives for a test to be
used over and over after reboots.

Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>