selftests: kvm: make hardware_disable_test less verbose

hardware_disable_test produces 512 snippets like
...
 main: [511] waiting semaphore
 run_test: [511] start vcpus
 run_test: [511] all threads launched
 main: [511] waiting 368us
 main: [511] killing child

and this doesn't have much value, let's print this info with pr_debug().

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210323104331.1354800-1-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>