LU-12661 tests: skip sanity 817 for kernel 4.12+

LU-12661 tests: skip sanity 817 for kernel 4.12+

Skip the NFS exec mode bug for kernels 4.12 and later, since this
is also being hit on SLES12/15 kernel 4.12.14+ and not just 4.14.

Lustre-change: https://review.whamcloud.com/39838
Lustre-commit: 3e2c28437404b0ccbd7bbfb8f77788678975b63d

Test-Parameters: trivial
Fixes: 4fed33473ca2 ("LU-12661 tests: skip sanity 817 if kernel >= 4.14")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Ibc4ffda72bd7827e250c4583c760505b8f3ebbe5
Reviewed-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/39863
Reviewed-by: Wei Liu <sarah@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>