LU-12622 tests: skip sanity test_816 with SSK

LU-12622 tests: skip sanity test_816 with SSK

sanity test_816 is incompatible with SSK, so skip it
in case SHARED_KEY is true.

Lustre-change: https://review.whamcloud.com/35664
Lustre-commit: b4ab1084cc0f1947ab65c32075d579edac5ab547

Whamcloud-bug-id: ATM-1283
Test-Parameters: trivial
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I019cf6a4bab8b0cf9825b7c49f364225d5156dfa
Reviewed-on: https://review.whamcloud.com/36401
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>