Description of problem:
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As decided, we will be deferring add/remove brick at this point wrt a tiered volume. 
Hence when a user tries to add/remove brick, it must fail or exit gracefully.
This bug is for tracking this purpose




Expected results:
================
Remove or add brick must exit or fail gracefully with proper error message if tried on a tiered volume only.

Additional info:
===============
this feature is planned to be disabled only for 3.7 gluster and should be available in future