rados/verify: crank up debugging on system tests

Looking for #5925

Signed-off-by: Sage Weil <sage@inktank.com>
mark all existing collections with %

This is ignored by old teuthology, but used by newer code to tell us when
to generate a product of all directory items.

Signed-off-by: Sage Weil <sage@inktank.com>
README: update for new flexible structure.

Signed-off-by: Sage Weil <sage@inktank.com>