generic/459: explicitly require thin_check

generic/459: explicitly require thin_check

The lvm command can invoke the thin pool utilities as part of
managing a thin volume. It'll fail if the thin provisioning
utilities are not installed, so we need to check for its presence
before running a test.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>