tests/qtest: get rid of some 'qtest_qmp' usage in migration test

Some of the usage is just a verbose way of re-inventing the
qtest_qmp_assert_success(_ref) methods.

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: <20230601161347.1803440-5-berrange@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
2 files changed