MEDIUM: servers: Be more agressive when adding H2 connection to idle lists.

MEDIUM: servers: Be more agressive when adding H2 connection to idle lists.

Add the newly created to the idle list as long as http-reuse != never, and
when completing a H2 request, add the connection to the safe list instead of
the idle list, if we have to add it at that point, that means we created
many streams so we know it's safe.