test_driver: Introduce testDomainObjCheckTaint

test_driver: Introduce testDomainObjCheckTaint

In order to test the virDomainGetMessages for test driver, we need to
check some taints or deprecations, so introduce testDomainObjCheckTaint
for checking taints.

As we introduced testDomainObjCheckTaint for test driver, the `dominfo`
command in virshtest will now print tainting messages, so add them for
test.

Signed-off-by: Luke Yue <lukedyue@gmail.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>