Fix tests_lvm_errors; skip vdo tests if dm-vdo not found

use volume1_size; check for expected error

https://bugzilla.redhat.com/show_bug.cgi?id=1990793
The test was using volume_size, which is undefined, instead
of volume1_size. Furthermore, the error was being masked by
the rescue block because the rescue was not checking for the
correct error message. The fix is to use volume1_size AND check
for the correct error message.

I'll note that there are several tests that do not look for the
correct error message, and we may run into this problem with other
tests.

skip test if kvdo and dm-vdo are not found

https://bugzilla.redhat.com/show_bug.cgi?id=1991062

Am getting this error when testing vdo:

Failed to commit changes to disk: Process reported exit code 3: modprobe: FATAL: Module dm-vdo not found in directory /lib/modules/5.14.0-0.rc4.35.el9.x86_64
  /usr/sbin/modprobe failed: 1
  vdo: Required device-mapper target(s) not detected in your kernel.
  Run `lvcreate --help' for more information.

So I'll just skip vdo testing unless both kvdo and dm-vdo are found.