Fix account metadata test for Ceph RadosGW Squid release

The test_list_no_account_metadata test was failing with Ceph RadosGW
19.2.x (Squid release) because it returns X-Account-Meta-Quota-Containers
as a system-generated header.

This change filters out the specific x-account-meta-quota-containers
header when checking for user-defined account metadata, allowing the
test to pass with both Swift and Ceph RadosGW backends while still
validating that no user-defined metadata headers are present.

Related ceph commit: https://github.com/ceph/ceph/commit/55f196cb47c9a452fc718ba9a58be7f68bb7a54a

Change-Id: Idbf22909b389190f7365bb3e54fd77d69df0c789
Signed-off-by: Maximilian Stinsky <maximilian.stinsky-damke@wiit.cloud>
1 file changed