cputest: Skip tests requiring JSON_MODELS if QEMU is disabled

cputest: Skip tests requiring JSON_MODELS if QEMU is disabled

Some tests require JSON_MODELS to be parsed into qemuCaps and applied
when computing CPU models and such test cannot succeed if QEMU driver is
disabled. Let's mark the tests with JSON_MODELS_REQUIRED and skip the
appropriate parts if building without QEMU.

On the other hand, CPU tests with JSON_MODELS should succeed even if
model definitions from QEMU are not parsed and applied. Let's explicitly
test this by repeating the tests without JSON_MODELS set.

This fixes the build with QEMU driver disabled, e.g., on some
architectures on RHEL/CentOS.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>