Make testclient creation idempotent

Change-Id: I55b4731b40abaf37b68a1642569929407f5ed19e
diff --git a/roles/test-client-install/files/test-client-playbook.yml b/roles/test-client-install/files/test-client-playbook.yml
index ab17491..fa13250 100644
--- a/roles/test-client-install/files/test-client-playbook.yml
+++ b/roles/test-client-install/files/test-client-playbook.yml
@@ -22,5 +22,4 @@
 
     - name: Create testclient
       become: yes
-      command: lxc-create -t ubuntu -n testclient
-
+      shell: lxc-ls | grep testclient || lxc-create -t ubuntu -n testclient