rgw: fix http error checks in keystone/barbican/vault clients

rgw: fix http error checks in keystone/barbican/vault clients

when RGWHTTPManager encounters an http error, it uses
rgw_http_error_to_errno() to map that to a negative posix error code.
RGWHTTPClient::process() returns that mapped error code, and exposes the
original http error via get_http_status()

the http client code for keystone, barbican, and vault were returning
early on the errors from process(), so weren't getting to the http error
checks

these clients now check for specific http errors before testing the
result of process()

Fixes: https://tracker.ceph.com/issues/62989
Signed-off-by: Casey Bodley <cbodley@redhat.com>