Fix checking of the [dns].nameservers value

This patch [1] introduced checking whether the CONF.dns.nameservers
is empty. If the CONF.dns.nameservers value is empty then the
initialization of the QueryClient fails. This change makes the majority
of designate-tempest-plugin tests fail even tests that do not use the
QueryClient.

This patch introduces three changes:

1) ValueError is raised only when the query() function is called so
   that only tests that actually use the query() function fail.

2) wait_for_query() function is fixed so that it never succeeds when the
   CONF.dns.nameservers value is empty.

3) Skip tests that rely upon [dns].nameserver value.

[1] https://review.opendev.org/c/openstack/designate-tempest-plugin/+/860116

Change-Id: Iedd151b2e47ed62adc168a97cb6021ccb47abb0f
diff --git a/designate_tempest_plugin/common/waiters.py b/designate_tempest_plugin/common/waiters.py
index affe332..cfa2d10 100644
--- a/designate_tempest_plugin/common/waiters.py
+++ b/designate_tempest_plugin/common/waiters.py
@@ -233,7 +233,7 @@
         else:
             all_answers_good = all(not r.answer for r in responses)
 
-        if not client.nameservers or all_answers_good:
+        if all_answers_good:
             LOG.info("Record %s of type %s was successfully %s on nameservers "
                      "%s", name, rdatatype, state, client.nameservers)
             return