Enable nose coverage support

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Add a bunch more config tests

And fix a couple of bugs found thereby.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Add coverage stats file to make clean target

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>