Scroll grafana pages to force all graphs to load

It appears that grafana won't load graph data if you don't scroll past
them in the window. Add a js execute script to each of the grafana
dashboard screenshot shots that scrolls to the bottom of the page in
order to force grafana to render each of the graphs on the page.

Change-Id: I12fb2992c3bca2c7ca85f6cedfef8fcdfd64d0a1

testinfra/test_grafana.py

@@ -47,12 +47,18 @@ def test_grafana_screenshots(host):
     cmd = host.run("curl -s --insecure "
                    "--resolve grafana.opendev.org:443:127.0.0.1 "
                    "https://grafana.opendev.org/api/search")
+    # Scroll to the bottom of the graph pages to force grafana to render each
+    # graph on the page. Adapted from:
+    # https://stackoverflow.com/questions/42982950/how-to-scroll-down-the-page-till-bottomend-page-in-the-selenium-webdriver
+    scroll_to_bottom = 'window.scrollTo(' \
+        '{top: document.body.scrollHeight, left: 0, behavior: "smooth"})'
     j = json.loads(cmd.stdout)
     for dashboard in j:
         url = dashboard["url"]
         uid = dashboard["uid"]
         name = dashboard["uri"].split("/")[-1]
-        shots.append(("https://localhost" + url, None, name + '.png'))
+        shots.append(
+            ("https://localhost" + url, scroll_to_bottom, name + '.png'))
         json_defs.append((uid, name + '.json'))
     take_screenshots(host, shots)
     host.run('mkdir /tmp/json_blobs')