Set mysql max_connections to 1024 on nodepool

Nodepool can end up with one connection per thread when dealing
with launches and deletions.  If we have a lot of node turnover,
that's a lot of threads.

Change-Id: Ice483f5f9f3a47963357f9ff59bf4d735a18aa43
Merge "Set mysql max_connections to 1024 on nodepool"