[AKS] remove k8s default version from CLI (#5456)

* [AKS] remove k8s default version from CLI

This allows the RP to set the default version if the user doesn't
supply one explicitly.

* Update HISTORY.rst for new `az aks create` default version behavior

* Fix some errant indentation.

src/command_modules/azure-cli-acs/HISTORY.rst

@@ -5,6 +5,7 @@ Release History
 
 2.0.26
 ++++++
+* `aks create` defaults to letting the server choose the version of Kubernetes
 * `aks create` VM node size default changed from "Standard_D1_v2" to "Standard_DS1_v2"
 * improve reliability when locating the dashboard pod for `az aks browse`
 

src/command_modules/azure-cli-acs/azure/cli/command_modules/acs/_help.py

@@ -166,7 +166,7 @@
           short-summary: Size in GB of the OS disk for each node in the node pool.
         - name: --kubernetes-version -k
           type: string
-          short-summary: Version of Kubernetes to use for creating the cluster, such as "1.7.7" or "1.8.2".
+          short-summary: Version of Kubernetes to use for creating the cluster, such as "1.7.12" or "1.8.6".
         - name: --ssh-key-value
           type: string
           short-summary: Public key path or key contents to install on node VMs for SSH access. For example,

src/command_modules/azure-cli-acs/azure/cli/command_modules/acs/_validators.py

@@ -71,14 +71,16 @@ def validate_create_parameters(namespace):
 
 
 def validate_k8s_version(namespace):
-    """Validates a string as a possible Kubernetes version."""
-    k8s_release_regex = re.compile(r'^[v|V]?(\d+\.\d+\.\d+.*)$')
-    found = k8s_release_regex.findall(namespace.kubernetes_version)
-    if found:
-        namespace.kubernetes_version = found[0]
-    else:
-        raise CLIError('--kubernetes-version should be the full version number, '
-                       'such as "1.7.7" or "1.8.1"')
+    """Validates a string as a possible Kubernetes version. An empty string is also valid, which tells the server
+    to use its default version."""
+    if namespace.kubernetes_version:
+        k8s_release_regex = re.compile(r'^[v|V]?(\d+\.\d+\.\d+.*)$')
+        found = k8s_release_regex.findall(namespace.kubernetes_version)
+        if found:
+            namespace.kubernetes_version = found[0]
+        else:
+            raise CLIError('--kubernetes-version should be the full version number, '
+                           'such as "1.7.12" or "1.8.6"')
 
 
 def validate_k8s_client_version(namespace):

src/command_modules/azure-cli-acs/azure/cli/command_modules/acs/custom.py

@@ -1253,7 +1253,7 @@ def aks_create(cmd, client, resource_group_name, name, ssh_key_value,  # pylint:
                dns_name_prefix=None,
                location=None,
                admin_username="azureuser",
-               kubernetes_version="1.7.7",
+               kubernetes_version='',
                node_vm_size="Standard_DS1_v2",
                node_osdisk_size=0,
                node_count=3,