query: Fix bug when names are specified

If the client/caller would specify names through the use of a filter,
the result would be sorted. This is a regression over earlier Ganeti
versions and verified in QA. This patch adds an optional parameter to
control the sorting and provides unittests.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>