Having the cookiejar available as attribute on the client instead of
some child objects exposes an interface which depending code can rely
on. This will help with upcoming efforts to switch the SOAP library
backing oslo.vmware.
This is part of phase 1 of
https://specs.openstack.org/openstack/oslo-specs/specs/victoria/oslo-vmware-soap-library-switch.html
Change-Id: I72082f10a184a2451dfda3d002a9288fefcef961