PXD-2731: Create Arborist client on client-create

[fantix]

This is the same PR as #610, requires uc-cdis/arborist#53.

[PlanXCyborg]

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--- fence/rbac/client.py
+++ blackened
@@ -390,11 +390,11 @@
                 "could not fetch client `{}` in arborist: {}".format(
                     client_id, data["error"]
                 )
             )
             raise ArboristError(data["error"])
-        current_policies = set(data['policies'])
+        current_policies = set(data["policies"])
         policies = set(policies)
 
         # find newly granted policies, revoke all if needed
         url = "/".join((self._client_url, client_id, "policy"))
         if current_policies.difference(policies):

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