Partial revert "Disable slow tests for kmemleak"

Enable zpool_clear_001_pos, zpool_create_024_pos and inherit_001_pos. These
are no longer slow.

Also disable zfs_destroy_001_pos, zfs_allow_010_pos and snapused_004_pos,
as they fail very often.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Closes #5613