Fixing an idempotency problem found in testing.

cluster/juju/charms/trusty/kubernetes-master/hooks/install.py

@@ -64,7 +64,10 @@ def clone_repository():
     """
 
     repository = 'https://github.com/GoogleCloudPlatform/kubernetes.git'
-    kubernetes_directory = '/opt/kubernetes'
+    kubernetes_directory = path('/opt/kubernetes')
+    # Since we can not clone twice, check for the directory and remove it.
+    if kubernetes_directory.isdir():
+        kubernetes_directory.rmtree_p()
 
     command = ['git', 'clone', repository, kubernetes_directory]
     print(command)