Fix burnin error of instance name retrieval

Switching to Haskell queries revealed a bug in burnin
regarding the fetching of instance names from queries.

Signed-off-by: Helga Velroyen <helgav@google.com>
Reviewed-by: Hrvoje Ribicic <riba@google.com>
Fix removal of duplicates

Commit ede6df3d02 introduced a bug in the node queries
where disk templates where paired up wrongly to their
storage unit keys due to removal of duplicates at the
wrong place. This patch fixes it.

Signed-off-by: Helga Velroyen <helgav@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>