Merge pull request #53454 from Cynerva/gkk/channel-1.8

Automatic merge from submit-queue (batch tested with PRs 53454, 53446, 52935, 53443, 52917). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Bump default snap channel to 1.8/stable in juju charms

**What this PR does / why we need it**:

This updates the Juju charms to deploy Kubernetes 1.8 by default.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

**Special notes for your reviewer**:

**Release note**:

```release-note
NONE
```

cluster/juju/layers/kubernetes-e2e/config.yaml

@@ -1,6 +1,6 @@
 options:
   channel:
     type: string
-    default: "1.7/stable"
+    default: "1.8/stable"
     description: |
       Snap channel to install Kubernetes snaps from

cluster/juju/layers/kubernetes-master/config.yaml

@@ -23,7 +23,7 @@ options:
       detected on a worker node.
   channel:
     type: string
-    default: "1.7/stable"
+    default: "1.8/stable"
     description: |
       Snap channel to install Kubernetes master services from
   client_password:

cluster/juju/layers/kubernetes-worker/config.yaml

@@ -22,7 +22,7 @@ options:
       switch to privileged mode if gpu hardware is detected.
   channel:
     type: string
-    default: "1.7/stable"
+    default: "1.8/stable"
     description: |
       Snap channel to install Kubernetes worker services from
   require-manual-upgrade: