Fix errors in lookup plugins.

Lookup plugins 'sequence' and 'template' now import 'ansible.utils'
appropriately in order to use the 'listify_lookup_plugin_terms'
function.

Also, 'dnstxt' and 'env' now check to see if 'terms' is a string;
without this calls like '{{ lookup('env', 'HOME') }}' fail.
Merge pull request #2700 from chamill/devel

Fix errors in lookup plugins.
Fix 'sequence' plugin error.

If 'terms' is a string, replace it with a single item list.
Merge pull request #2701 from chamill/devel

Fix 'sequence' plugin error.
Fix if-statement that always evaluates True
Merge pull request #2705 from b6d/utils-fix

Fix if-statement that always evaluates True
(A) include errors in inventory scripts should they occur.

(B) allow registration with ignore_errors: True
correct reference to module
Merge pull request #2712 from lwade/devel

correct reference to module