Set up examples gate job for 1.11 (#9345)

There were things changed upstream which have blocked the examples test
from running correctly:

- PodSecurityPolicy has been MOVED from extensions API group into
  policy. All samples that are using this resource type needs a change.
- The 'GetCodecForObject()' function in testapi/testapi package was
  removed in 1.11 for unknown reasons. This change has broken our job as
  well as the test code in the kubernetes/examples project.
- Kubernetes is now using 1.10.2+ verion of Go for compilation so we
  have to change the .travis.yml accordingly.

This PR fixes the above problems.

Note also, the `TestReadme` function is **removed** for two reasons:

- It is only testing the snippets in the `volumes.md` file which is now
  broken because of the introduction of service account token injection.
- It is regarded as too aggressive/restrictive a test. We cannot
  guarantee that YAML snippets in the markdown files are complete and
  can be used as is. Instead I believe we should encourage people to use
  template snippets that contain the **key** information for a topic.
  When we see a need for a full template that can be used directly, we
  may want to extract the YAML contents into the `examples`
  subdirectory.

.travis.yml

@@ -1,6 +1,6 @@
 language: go
 go:
-  - 1.9.3
+  - 1.10.2
 
 # Don't want default ./... here:
 install:
@@ -10,7 +10,7 @@ install:
 # Fetch dependencies for us to run the tests in test/examples_test.go
 - go get -t -v k8s.io/website/test
 # Make sure we are testing against the correct branch
-- pushd $GOPATH/src/k8s.io/kubernetes && git checkout release-1.10 && popd
+- pushd $GOPATH/src/k8s.io/kubernetes && git checkout release-1.11 && popd
 
 # Simplified deduplication of dependencies.
 - cp -L -R $GOPATH/src/k8s.io/kubernetes/vendor/ $GOPATH/src/