py3: Update Shared.DC.ZRDB.{sqltest,sqlvar} monkey patches.

This supports both python2 and python3. For python3, this decode() properly
arguments returned by string_literal() to have str(), otherwise the query string
is an str() (DocumentTemplate) and the arguments are bytes().

In other places, bytes() is used directly but in this case this is not needed
and would require monkey patching (at least) DocumentTemplate.