bug#43826: cuirass: build query is too slow.

[Mathieu Othacehe]

Hello,

When "db-get-builds" is called with a limit set to N, at least ~2N
queries are executed. First the main query returns the build list, then
build outputs and build products are searched.

All of this should be combined in a unique query to minimize
overhead. The limit should also by restricted to at most 1000 builds for
instance.

Thanks,

Mathieu