Try to reduce mysql memory usage

These are a few tweaks I applied to my own memory-constrained cloud
instances that seemed to help. I have lower performance requirements
so this may make things worse and not better, but it's worth seeing
what the impact is. I'll admit to not knowing the full impact of these
as they're mostly collected from various tutorials on lowering memory
usage.

Enable this for now on devstack-multinode

Change-Id: I7b223391d3de01e3e81b02076debd01d9d2f097c
diff --git a/stackrc b/stackrc
index a05d1e5..442e9a0 100644
--- a/stackrc
+++ b/stackrc
@@ -201,6 +201,11 @@
 # performance_schema that are of interest to us
 MYSQL_GATHER_PERFORMANCE=$(trueorfalse True MYSQL_GATHER_PERFORMANCE)
 
+# This can be used to reduce the amount of memory mysqld uses while running.
+# These are unscientifically determined, and could reduce performance or
+# cause other issues.
+MYSQL_REDUCE_MEMORY=$(trueorfalse False MYSQL_REDUCE_MEMORY)
+
 # Set a timeout for git operations.  If git is still running when the
 # timeout expires, the command will be retried up to 3 times.  This is
 # in the format for timeout(1);