[Service Bus] Rename ServiceBusManagementClient class to ServiceBusAdministrationClient

[ramya-rao-a]

The naming guidelines for a client that does resource management but not via the ARM apis, is that it should use the term Administration and not Management. See Azure/azure-sdk#1360 for more details

For this reason, the ServiceBusManagementClient class in the new Service Bus package which is currently in preview should be renamed to ServiceBusAdministrationClient