configuration-reload-test: wait for the new worker to get ready

After sending a SIGHUP, wait for the new worker process with the
new configuration to handle further requests, or else the tests
running after that might get confused when the new worker becomes
active with fresh shared mem statistics and shared mem cache.

test/nginx_system_test.sh

@@ -302,6 +302,9 @@ fi
 #
 # TODO(sligicki): When the prioritize critical css race condition is fixed, the
 # two prioritize_critical_css tests no longer need to be listed here.
+# TODO(oschaaf): Now that we wait after we send a SIGHUP for the new worker 
+# process to handle requests, check if we can remove more from the expected 
+# failures here under valgrind.
 if $USE_VALGRIND; then
     PAGESPEED_EXPECTED_FAILURES+="
 ~combine_css Maximum size of combined CSS.~
@@ -310,7 +313,6 @@ if $USE_VALGRIND; then
 ~IPRO flow uses cache as expected.~
 ~IPRO flow doesn't copy uncacheable resources multiple times.~
 ~inline_unauthorized_resources allows unauthorized css selectors~
-~Blocking rewrite enabled.~
 "
 fi
 
@@ -551,6 +553,14 @@ fire_ab_load
 check wget $EXAMPLE_ROOT/styles/W.rewrite_css_images.css.pagespeed.cf.Hash.css \
   -O /dev/null
 check_simple "$NGINX_EXECUTABLE" -s reload -c "$PAGESPEED_CONF"
+# Wait for the new worker process with the new configuration to get ready, or
+# else the sudden reset of the shared mem statistics/cache might catch upcoming
+# tests unaware.
+while [ $(scrape_stat image_rewrite_total_original_bytes) -gt 0 ]
+do
+    echo "Waiting for new worker to get ready..."
+    sleep .1
+done
 
 check wget $EXAMPLE_ROOT/styles/W.rewrite_css_images.css.pagespeed.cf.Hash.css \
   -O /dev/null