rgw: don't require system pools to start with a period

rgw: don't require system pools to start with a period

Make sure cache operations are being done on system objects.
Separate calls where needed to make sure that separate pool/bucket
handling is done correctly. When separating calls, don't use objv_tracker
for data objects, don't use data constructs for system objects.

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>