rgw: add logging to bucket listing so calls are better understood

rgw: add logging to bucket listing so calls are better understood

The logic to bucket listing is complex due to the sharded bucket
indicies. When a log is examined, there should be enough information
to follow the logic.

Logging that touches every entry listed is at 20. Logging that
describes exiting of the listing are at level 10.

Additionally make logging more uniform and streamlined. Remove "INFO"
as that seems redundant (but keep "ERROR" and "WARNING"). Dispense
with class name decorating function name since there aren't any
similar function names.

Signed-off-by: J. Eric Ivancich <ivancich@redhat.com>