Replace $tenant usage in CollectionCloner.

Currently, this "$tenant" is used for command "callStats", the command body looks like 

{    callStats: collname,    $db: dbname (non tenant prefixed),    $tenant: tenantId, }

We need to replace "$tenant" with unsigned security token. The command body looks like

{    callStats: collname,    $db: dbname (non tenant prefixed), }

. The command also include an unsigned security token which has no "expectPrefix".