Fix tempest logging configuration

This commit will correctly set the tempest output logging to dump
all of tempest logs into a tempest.log file in
$DEST/tempest/tempest.log. This will also fix the logging for
tempest in the gate so it will no longer print every log message on
the console.

Fixes bug 1207066

Change-Id: I91f2ee781c4a7a18c561ea3e3b26832b97431464
diff --git a/lib/tempest b/lib/tempest
index 6c68337..aaa7281 100644
--- a/lib/tempest
+++ b/lib/tempest
@@ -199,6 +199,8 @@
     # Oslo
     iniset $TEMPEST_CONF DEFAULT lock_path $TEMPEST_STATE_PATH
     mkdir -p $TEMPEST_STATE_PATH
+    iniset $TEMPEST_CONF DEFAULT use_stderr False
+    iniset $TEMPEST_CONF DEFAULT log_file tempest.log
 
     # Timeouts
     iniset $TEMPEST_CONF compute build_timeout $BUILD_TIMEOUT