Fix: namespace-create have kubectl in path

cluster/juju/layers/kubernetes-master/actions/namespace-create

 #!/usr/bin/env python3
-
+import os
 from yaml import safe_load as load
 from charmhelpers.core.hookenv import (
     action_get,
@@ -11,6 +11,9 @@ from charms.templating.jinja2 import render
 from subprocess import check_output
 
 
+os.environ['PATH'] += os.pathsep + os.path.join(os.sep, 'snap', 'bin')
+
+
 def kubectl(args):
     cmd = ['kubectl'] + args
     return check_output(cmd)