The function is renamed as virQEMUCapsProbeHostCPU and it does not get
the list of allowed CPU models from qemuCaps anymore. This is
responsibility is moved to the caller. The result is just a very thin
wrapper around virCPUGetHost mostly required mocking in tests.

The generic function is used in place of a direct call to virCPUGetHost
in virQEMUCapsInitHostCPUModel to make sure tests don't accidentally
probe host CPU.
Signed-off-by: NJiri Denemark <jdenemar@redhat.com>