LU-12894 sec: fix checksum for skpi

LU-12894 sec: fix checksum for skpi

Compute checkum on message before actually comparing
it to hmac value.

Add test to exercise all SSK flavors.
Make sure zconf_mount does include skpath mount option if SSK or
Kerberos is in use.

Lustre-change: https://review.whamcloud.com/36604
Lustre-commit: dcdf060342e7d69b64171840cf9475bf65d036ea

Fixes: a21c13d4df ("LU-8602 gss: Properly port gss to newer crypto api.")
Test-Parameters: envdefinitions=SHARED_KEY=true testlist=sanity-sec
Test-Parameters: envdefinitions=SHARED_KEY=true,SK_FLAVOR=skn testlist=sanity,recovery-small
Test-Parameters: envdefinitions=SHARED_KEY=true,SK_FLAVOR=ska testlist=sanity,recovery-small
Test-Parameters: envdefinitions=SHARED_KEY=true,SK_FLAVOR=ski testlist=sanity,recovery-small
Test-Parameters: envdefinitions=SHARED_KEY=true,SK_FLAVOR=skpi testlist=sanity,recovery-small
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I7bcc3618c1824a0f0ca73219c7ac0ccc8405b946
Reviewed-on: https://review.whamcloud.com/37028
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>