Dont call READCAPACITY from every single test.
Remove two arguments from the test signatures and turn them into globals.
remove the ret++ silliness. Tests return 0 : all ok, -2, skipped or -1 : test failed
0171 is expecting a 0-block unmap at end-of-volume (i.e. start block
one beyond what READ CAPACITY returns) to pass, while every other 0blocks
test is expecting that address to be invalid.
