softmmu/vl: Be less verbose about missing KVM when running the qtests

softmmu/vl: Be less verbose about missing KVM when running the qtests

Some of the qtests use "-accel kvm -accel tcg" to run real guest code.
This causes some error messages when kvm is not available. We do not
really care about these messages since the fallback to tcg is expected
here. So let's silence them to avoid that they spoil the output of
the tests.

Unfortunately, we can not use the qtest_enabled() wrapper in this case,
since the qtest accelerator itself is not initialized. Thus we have to
test for the qtest_chrdev variable instead.

Message-Id: <20200710085020.28222-1-thuth@redhat.com>
Reviewed-by: Alexander Bulekov <alxndr@bu.edu>
Signed-off-by: Thomas Huth <thuth@redhat.com>