tasks/cephfs/mount: use seperate for testing flock and posix lock

Old version libfuse treats both flock and posix lock requests as posix
lock request. This is a workaround for the bug.

Fixes: #9995
Signed-off-by: Yan, Zheng <zyan@redhat.com>
Merge pull request #228 from ceph/wip-9995

tasks/cephfs/mount: use seperate for testing flock and posix lock

Reviewed-by: John Spray <john.spray@redhat.com>