ceph_objectstore_tool: Bug fixes and test improvements

ceph_objectgstore_tool:
Fix bugs in the way collection_list_partial() was being called
which caused objects to be seen over and over again.

Unit test:
Fix get_objs() to walk pg tree for pg with sub-directories
Create more objects to test object listing code
Limit number of larger objects
Limit number of objects which get attributes and omaps

Signed-off-by: David Zafman <dzafman@redhat.com>