Remove unused exceptions
Remove unused exceptions

Before this patch, exceptions.py is synced with Tempest's exceptions.py.
However, it is difficult to do it now because rest_client raises its own
exceptions on tempest-lib and Tempest should handle them without Tempest's
exceptions.
This patch removes unused exceptions in tempest-lib for knowing tempest-lib
own exceptions easily.

Change-Id: I435f0752685f54e6b86d1f243a5236d79c9e250c

sorenh/tempest-lib,JioCloud/tempest-lib,cneill/tempest-lib,afaheem88/tempest-lib,varunarya10/tempest-lib