ci(aio): move e2e tests to non-optional job

This essentially reverts #20178, since the flakes should be gone after
pinning ChromeDriver and Chrome versions to 2.32 and 59 respectively.

scripts/ci/test-aio.sh

@@ -31,6 +31,12 @@ source ${thisDir}/_travis-fold.sh
   travisFoldEnd "test.aio.unit"
 
 
+  # Run e2e tests
+  travisFoldStart "test.aio.e2e"
+    yarn e2e
+  travisFoldEnd "test.aio.e2e"
+
+
   # Run unit tests for aio/aio-builds-setup
   travisFoldStart "test.aio.aio-builds-setup"
     ./aio-builds-setup/scripts/test.sh