Compress stackviz data

Each stackviz "install" needs about 15MB of disk, a significant portion
of which is just json data that is rendered. We can compress that as
long as our server knows to serve .json.gz when asked for .json files
(and it should, but this serves as a self testing check of that).

Change-Id: Ie0f25f06bdd539945f5f9c26885f0388354bd129

functions.sh

@@ -600,6 +600,8 @@ function process_stackviz {
                 $log_path/stackviz/data
         fi
         sudo chown -R $USER:$USER $log_path/stackviz
+        # Compress the stackviz data as it is quite large.
+        sudo find $log_path/stackviz -iname '*.json' -execdir gzip -9 {} \+
         popd
     fi
 }