engine/rados: Add option to skip object creation

engine/rados: Add option to skip object creation

When `touch_objects` is false, connection procedure no longer attempts to create objects.
In such case ceph caches are untouched and do not affect quality of performance measurement.
But if `touch_object` is false, tests that read objects without creating them previously
will now fail.

Signed-off-by: Adam Kupczyk <akupczyk@redhat.com>