Set join_cache_level = 2 for labsdbs.

An as-yet-unidentified query on labsdb1003 causes a segfault. Going
by the stack trace it is a poorly indexed SELECT using a
block-based join and multi-range read when join_cache_level > 2.

Change-Id: I61dbefe13af4b910857ea0ecfc2d3b985d8fc08b