Default MYSQL_REDUCE_MEMORY=True

We have lots of evidence that this is a net benefit, so enable it
by default instead of everyone having to opt-in.

Change-Id: I66fa1799ff5177c3667630a89e15c072a8bf975a
diff --git a/.zuul.yaml b/.zuul.yaml
index 316e89a..9cad5d4 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -696,9 +696,6 @@
     description: |
       Simple multinode test to verify multinode functionality on devstack side.
       This is not meant to be used as a parent job.
-    vars:
-      devstack_localrc:
-        MYSQL_REDUCE_MEMORY: true
 
 # NOTE(ianw) Platform tests have traditionally been non-voting because
 # we often have to rush things through devstack to stabilise the gate,
diff --git a/stackrc b/stackrc
index b7ce238..672679e 100644
--- a/stackrc
+++ b/stackrc
@@ -204,7 +204,7 @@
 # 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=$(trueorfalse False MYSQL_REDUCE_MEMORY)
+MYSQL_REDUCE_MEMORY=$(trueorfalse True 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