Fix libvirt driver tests to use LibvirtConfigCapsGuest instances
Fix libvirt driver tests to use LibvirtConfigCapsGuest instances

test_driver.LibvirtConnTestCase.test_cpu_info() and
test_driver.LibvirtConnTestCase.test_get_instance_capabilities() were
incorrectly adding LibvirtConfigGuest fixture objects to the guests
attribute of LibvirtConfigCaps, rather than LibvirtConfigCapsGuest
objects which is what the parse_dom() method of LibvirtConfigCaps
does.  LibvirtConfigCaps is intended to capture all useful information
returned by libvirt's getCapabilities API call, and
LibvirtConfigCapsGuest is intended to capture a small subset of that.
In contrast, LibvirtConfigGuest is intended for holding the entire
configuration of a libvirt guest domain.

So fix this to instead add LibvirtConfigCapsGuest fixtures.

Note that despite this bug, the tests previously passed through
duck-typing because LibvirtConfigCaps does not define __slots__ or any
other mechanism for limiting how attributes can be set on instances.

This is required by another commit in the SEV series in the near
future which will alter the fields within LibvirtConfigCapsGuest.

blueprint: amd-sev-libvirt-support
Change-Id: Ic4cbbaf81938fc88980e44c4a17fe388f9c2b92b

klmitch/nova,klmitch/nova,mahak/nova,openstack/nova,openstack/nova,rahulunair/nova,rahulunair/nova,klmitch/nova,rahulunair/nova,openstack/nova,mahak/nova,mahak/nova,klmitch/nova