search_next: Minor speed optimization.
search_next: Minor speed optimization.

Instead of constructing full objects when scanning for the next
available label, restrict the query to returning just the labels.

Reviewed-By: Gabor Gombas <3bb8c49439d9d044594e1c6967f991d0b4248a64@morganstanley.com>

stdweird/aquilon,stdweird/aquilon,guillaume-philippon/aquilon,quattor/aquilon,quattor/aquilon,guillaume-philippon/aquilon,quattor/aquilon,guillaume-philippon/aquilon,stdweird/aquilon