Fix bug in a test for the scheduler DiskFilter.
Fix bug in a test for the scheduler DiskFilter.

There is an error in the logic for a unit test in the Scheduler DiskFilter.
We need to test the failure of the host_passes check with the
"test_disk_filter_fails" test.

Fixes bug 1070264.

Change-Id: Ib07f47b74a6634c573dca8fb4efa2d95b2e1ed87

n0ano/gantt,n0ano/gantt