generate_tests: Use "latest" markers instead of "k8s-*" pseudo-versions

The "k8s-beta" version marker leads to confusion as sometimes "beta"
should refer to the current pre-release branch and sometimes it should
point to master. There is no consistent guidance or follow-through on
how or when these markers need to be changed, which can lead to a slew
of tests that don't test what we think they do.

As a first step, we're setting test_config.yaml to use the "latest**"
version markers, which are pretty clear at a glance which version of
Kubernetes will be tested against:

- "dev" --> "latest" --> 1.18.0-ish
- "beta" --> "latest" --> 1.18.0-ish
- "stable1" --> "latest-1.16" --> 1.16-ish
- "stable2" --> "latest-1.15" --> 1.15-ish
- "stable3" --> "latest-1.14" --> 1.14-ish

Note that "beta" here was shifted back to be even with "dev" since we've
just finished cutting the 1.17.0 release.

Signed-off-by: Stephen Augustus <[email protected]>

experiment/test_config.yaml

@@ -810,19 +810,19 @@ k8sVersions:
     version: master
   beta:
     args:
-    - --extract=ci/k8s-beta
-    version: '1.17'
+    - --extract=ci/latest
+    version: master
   stable1:
     args:
-    - --extract=ci/k8s-stable1
+    - --extract=ci/latest-1.16
     version: '1.16'
   stable2:
     args:
-    - --extract=ci/k8s-stable2
+    - --extract=ci/latest-1.15
     version: '1.15'
   stable3:
     args:
-    - --extract=ci/k8s-stable3
+    - --extract=ci/latest-1.14
     version: '1.14'
 
 testSuites:
@@ -932,23 +932,23 @@ nodeK8sVersions:
   dev:
     args:
     - --repo=k8s.io/kubernetes=master
-    prowImage: gcr.io/k8s-testimages/kubekins-e2e:v20191211-04e540b-master
+    prowImage: gcr.io/k8s-testimages/kubekins-e2e:v20191209-15bc109-master
   beta:
     args:
-    - --repo=k8s.io/kubernetes=release-1.17
-    prowImage: gcr.io/k8s-testimages/kubekins-e2e:v20191211-04e540b-1.17
+    - --repo=k8s.io/kubernetes=master
+    prowImage: gcr.io/k8s-testimages/kubekins-e2e:v20191209-15bc109-master
   stable1:
     args:
     - --repo=k8s.io/kubernetes=release-1.16
-    prowImage: gcr.io/k8s-testimages/kubekins-e2e:v20191211-04e540b-1.16
+    prowImage: gcr.io/k8s-testimages/kubekins-e2e:v20191209-15bc109-1.16
   stable2:
     args:
     - --repo=k8s.io/kubernetes=release-1.15
-    prowImage: gcr.io/k8s-testimages/kubekins-e2e:v20191211-04e540b-1.15
+    prowImage: gcr.io/k8s-testimages/kubekins-e2e:v20191209-15bc109-1.15
   stable3:
     args:
     - --repo=k8s.io/kubernetes=release-1.14
-    prowImage: gcr.io/k8s-testimages/kubekins-e2e:v20191211-04e540b-1.14
+    prowImage: gcr.io/k8s-testimages/kubekins-e2e:v20191209-15bc109-1.14
 
 nodeTestSuites:
   default: