When running in TAP mode, stdout is reserved for the TAP protocol.
To see the "diff" of the failed test, we have to print it to
stderr instead.
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20220209101530.3442837-8-thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>