Improve debug logging around dynamic layout loading

This will give us a better idea of how much time we're spending.

Change-Id: Idbd4a8b61664d3d3af0534fb0d3f24e21808ad5a
diff --git a/zuul/manager/__init__.py b/zuul/manager/__init__.py
index b94b8a5..2cb34b8 100644
--- a/zuul/manager/__init__.py
+++ b/zuul/manager/__init__.py
@@ -435,12 +435,12 @@
         loader = zuul.configloader.ConfigLoader()
 
         build_set = item.current_build_set
-        self.log.debug("Loading dynamic layout")
         try:
             # First parse the config as it will land with the
             # full set of config and project repos.  This lets us
             # catch syntax errors in config repos even though we won't
             # actually run with that config.
+            self.log.debug("Loading dynamic layout (phase 1)")
             loader.createDynamicLayout(
                 item.pipeline.layout.tenant,
                 build_set.files,
@@ -450,10 +450,12 @@
 
             # Then create the config a second time but without changes
             # to config repos so that we actually use this config.
+            self.log.debug("Loading dynamic layout (phase 2)")
             layout = loader.createDynamicLayout(
                 item.pipeline.layout.tenant,
                 build_set.files,
                 include_config_projects=False)
+            self.log.debug("Loading dynamic layout complete")
         except zuul.configloader.ConfigurationSyntaxError as e:
             self.log.info("Configuration syntax error "
                           "in dynamic layout")