LU-12679 tests: large-lun test_2 check OSTSIZE or skip (zfs)

LU-12679 tests: large-lun test_2 check OSTSIZE or skip (zfs)

Ensure OSTSIZE is sufficient for test to run, or the
backing device is sufficient, otherwise skip the test.

Use the zfs pool name when invoking zdb to report the
super block details.

Cray-bug-id: LUS-6875
Test-Parameters: fstype=zfs testlist=large-lun envdefinitions=REFORMAT=yes
Signed-off-by: Shaun Tancheff <stancheff@cray.com>
Change-Id: I65d8bac11d437230153c6ad8d821a5372244f7fa
Reviewed-on: https://review.whamcloud.com/35854
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Petros Koutoupis <pkoutoupis@cray.com>
Reviewed-by: Ben Evans <bevans@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>