LU-18162 kunit: convert LDLM extent test to LU device

LU-18162 kunit: convert LDLM extent test to LU device

Convert LDLM extent test to use LU device init/fini rather
than the legacy OBD API.

Test-Parameters: trivial env=SLOW=yes env=ONLY=842 testlist=sanity
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: Id043fc2e768b2447cee582be4dc0d5032ec57882
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/58804
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>