vpp_papi: Add custom exceptions.
This patchset adds and raises the following custom exception classes:
* class VPPApiError(Exception):
* class VPPNotImplementedError(NotImplementedError):
* class VPPIOError(IOError):
* class VPPRuntimeError(RuntimeError):
* class VPPValueError(ValueError):
* class VPPSerializerValueError(ValueError):
* class VPPStatsIOError(IOError):
* class VPPStatsClientLoadError(RuntimeError):
* class VppTransportShmemIOError(IOError):
* class VppTransportSocketIOError(IOError)
Change-Id: Ia40900fd2dcef148d01125d6c691329fc666901e
Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>