Bump nodepool's file descriptor limit.

Nodepool is running into file descriptor limits like Zuul. Again
compromise and bump the limit in the init script to give us breathing
room until the problem can be properly fixed.

Change-Id: Idd1fd679bdad1d3ea4951be7f9330214d7065027
Bump mysql connection limit for nodepool.

Nodepool is having its file descriptor limit bumped to 8192. Bump the
mysql connection limit to match to avoid having trouble on the other
side.

Change-Id: Ic164bddc860f8f569a2a0acb5290aaeb775bdd9a