dashboard: auto-update builder.sh.

avoid possibility of busy loop pounding on dashboard.

R=agl1
CC=golang-dev
https://golang.org/cl/206051

misc/dashboard/buildcron.sh

@@ -41,6 +41,9 @@ fi
 if [ ! -d $GOROOT ]; then
 	mkdir -p $GOROOT
 	hg clone https://go.googlecode.com/hg/ $GOROOT
+else
+	cd $GOROOT
+	hg pull -u || exit 1
 fi
 mkdir -p $GOROOT/bin
 

misc/dashboard/builder.sh

@@ -74,4 +74,5 @@ while true ; do
         fi
     fi
     cd ../.. || fatal "Cannot cd up"
+    sleep 10
 done