tests: Remove unnecessary global_qtest references

We are going to remove global_qtest from the main libqtest library
soon, so tests that do not urgently need global_qtest anymore
should be cleaned from the unnecessary references.

Message-Id: <20190904130047.25808-5-thuth@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>