qtest_start() + qtest_end() should be avoided, since they use the
global_qtest variable that we want to get rid of in the long run
Use qtest_init() and qtest_quit() instead.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20190409085245.31548-5-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>