Add shelltests verifying hail applies disk ipolicy per disk

Add shelltests verifying hail applies disk ipolicy per disk

We test on two minimal examples, a positive and a negative one, where
the possibility to allocate a node depends on whether the disk policy
is checked on a per-disk level or on the total amount of disk space
requested.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>