Gather performance data after tempest

This makes us gather a bunch of consistent statistics after we run
tempest that can be use to measure the impact of a given change. These
are stable metrics such as "number of DB queries made" and "how much
memory is each service using after a tempest run."

Note that this will always run after devstack to generate the JSON
file, but there are two things that control its completeness:

 - MYSQL_GATHER_PERFORMANCE must be enabled to get per-db stats
 - Unless tls-proxy is enabled, we will only get API stats for keystone

Change-Id: Ie3b1504256dc1c9c6b59634e86fa98494bcb07b1
diff --git a/stackrc b/stackrc
index d22fa88..c3254dc 100644
--- a/stackrc
+++ b/stackrc
@@ -193,6 +193,10 @@
 # (currently only implemented for MySQL backend)
 DATABASE_QUERY_LOGGING=$(trueorfalse False DATABASE_QUERY_LOGGING)
 
+# This can be used to turn on various non-default items in the
+# performance_schema that are of interest to us
+MYSQL_GATHER_PERFORMANCE=$(trueorfalse True MYSQL_GATHER_PERFORMANCE)
+
 # 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);