tests/qtest: replace wait_command() with qtest_qmp_assert_success

Most usage of wait_command() is followed by qobject_unref(), which
is just a verbose re-implementation of qtest_qmp_assert_success().

Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20230601161347.1803440-7-berrange@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
3 files changed