Fix GCE channels version constraints

Previously k8s 1.17+ would always match with COS rather than Ubuntu 20.04 because of the unbound version range.

This should fix the failure to download logs via SSH here: https://prow.k8s.io/view/gs/kubernetes-jenkins/logs/e2e-kops-gce-kubetest2/1373013584195358720
The instance groups confirm the use of COS rather than u2004: https://storage.googleapis.com/kubernetes-jenkins/logs/e2e-kops-gce-kubetest2/1373013584195358720/artifacts/instancegroups.yaml

channels/alpha

@@ -73,7 +73,7 @@ spec:
     - name: "cos-cloud/cos-stable-77-12371-114-0"
       providerID: gce
       architectureID: amd64
-      kubernetesVersion: ">=1.16.0-alpha.1"
+      kubernetesVersion: ">=1.16.0 <1.17.0"
     - name: "ubuntu-os-cloud/ubuntu-2004-focal-v20210119a"
       providerID: gce
       architectureID: amd64

channels/stable

@@ -73,7 +73,7 @@ spec:
     - name: "cos-cloud/cos-stable-77-12371-114-0"
       providerID: gce
       architectureID: amd64
-      kubernetesVersion: ">=1.16.0-alpha.1"
+      kubernetesVersion: ">=1.16.0 <1.17.0"
     - name: "ubuntu-os-cloud/ubuntu-2004-focal-v20210119a"
       providerID: gce
       architectureID: amd64

tests/integration/create_cluster/gce_byo_sa/expected-v1alpha2.yaml

@@ -62,7 +62,7 @@ metadata:
     kops.k8s.io/cluster: gce.example.com
   name: master-us-test1-a
 spec:
-  image: cos-cloud/cos-stable-77-12371-114-0
+  image: ubuntu-os-cloud/ubuntu-2004-focal-v20210119a
   machineType: n1-standard-1
   maxSize: 1
   minSize: 1
@@ -85,7 +85,7 @@ metadata:
     kops.k8s.io/cluster: gce.example.com
   name: nodes-us-test1-a
 spec:
-  image: cos-cloud/cos-stable-77-12371-114-0
+  image: ubuntu-os-cloud/ubuntu-2004-focal-v20210119a
   machineType: n1-standard-2
   maxSize: 1
   minSize: 1

tests/integration/create_cluster/ha_gce/expected-v1alpha2.yaml

@@ -70,7 +70,7 @@ metadata:
     kops.k8s.io/cluster: ha-gce.example.com
   name: master-us-test1-a
 spec:
-  image: cos-cloud/cos-stable-77-12371-114-0
+  image: ubuntu-os-cloud/ubuntu-2004-focal-v20210119a
   machineType: n1-standard-1
   maxSize: 1
   minSize: 1
@@ -93,7 +93,7 @@ metadata:
     kops.k8s.io/cluster: ha-gce.example.com
   name: master-us-test1-b
 spec:
-  image: cos-cloud/cos-stable-77-12371-114-0
+  image: ubuntu-os-cloud/ubuntu-2004-focal-v20210119a
   machineType: n1-standard-1
   maxSize: 1
   minSize: 1
@@ -116,7 +116,7 @@ metadata:
     kops.k8s.io/cluster: ha-gce.example.com
   name: master-us-test1-c
 spec:
-  image: cos-cloud/cos-stable-77-12371-114-0
+  image: ubuntu-os-cloud/ubuntu-2004-focal-v20210119a
   machineType: n1-standard-1
   maxSize: 1
   minSize: 1
@@ -139,7 +139,7 @@ metadata:
     kops.k8s.io/cluster: ha-gce.example.com
   name: nodes-us-test1-a
 spec:
-  image: cos-cloud/cos-stable-77-12371-114-0
+  image: ubuntu-os-cloud/ubuntu-2004-focal-v20210119a
   machineType: n1-standard-2
   maxSize: 1
   minSize: 1
@@ -162,7 +162,7 @@ metadata:
     kops.k8s.io/cluster: ha-gce.example.com
   name: nodes-us-test1-b
 spec:
-  image: cos-cloud/cos-stable-77-12371-114-0
+  image: ubuntu-os-cloud/ubuntu-2004-focal-v20210119a
   machineType: n1-standard-2
   maxSize: 1
   minSize: 1
@@ -185,7 +185,7 @@ metadata:
     kops.k8s.io/cluster: ha-gce.example.com
   name: nodes-us-test1-c
 spec:
-  image: cos-cloud/cos-stable-77-12371-114-0
+  image: ubuntu-os-cloud/ubuntu-2004-focal-v20210119a
   machineType: n1-standard-2
   maxSize: 1
   minSize: 1

tests/integration/create_cluster/private_gce/expected-v1alpha2.yaml

@@ -72,7 +72,7 @@ metadata:
     kops.k8s.io/cluster: private.example.com
   name: bastions
 spec:
-  image: cos-cloud/cos-stable-77-12371-114-0
+  image: ubuntu-os-cloud/ubuntu-2004-focal-v20210119a
   machineType: f1-micro
   maxSize: 1
   minSize: 1
@@ -98,7 +98,7 @@ spec:
   additionalSecurityGroups:
   - sg-exampleid3
   - sg-exampleid4
-  image: cos-cloud/cos-stable-77-12371-114-0
+  image: ubuntu-os-cloud/ubuntu-2004-focal-v20210119a
   machineType: n1-standard-1
   maxSize: 1
   minSize: 1
@@ -124,7 +124,7 @@ spec:
   additionalSecurityGroups:
   - sg-exampleid
   - sg-exampleid2
-  image: cos-cloud/cos-stable-77-12371-114-0
+  image: ubuntu-os-cloud/ubuntu-2004-focal-v20210119a
   machineType: n1-standard-2
   maxSize: 1
   minSize: 1