Add a shared volume for WebDriver's socket

.drone.jsonnet

@@ -141,6 +141,9 @@ local Unit(db) = cachedPipeline(
 // It installs a local instance an run integration test with Python scripts
 // that use Selenium (located in scripts/browser_test).
 local Integration(db) = {
+    volumes: [
+        name: 'webdriver-socket', temp: {},
+    ]
 } + basePipeline(
     "integration-" + db,
     [
@@ -150,6 +153,9 @@ local Integration(db) = {
             name: 'selenium',
             image: 'elgalu/selenium:latest',
             detach: true,
+            volumes: [
+                { name: 'webdriver-socket', path: '/wd' },
+            ]
         },
         {
             name: "integration-" + db,
@@ -158,6 +164,9 @@ local Integration(db) = {
                 BROWSER: "firefox",
                 DATABASE_URL: if db == "postgres" then "postgres://plume:password@start-db/plume" else "plume.db",
             },
+            volumes: [
+                { name: 'webdriver-socket', path: '/wd' },
+            ],
             commands: [
                 // Install the front-end
                 "cargo web deploy -p plume-front",