removes self.fail as suggested by HACKING.rst

removes every occurrence of self.fail as per HACKING.rst file; it
is either replaced with a LOG+raise or removed completely when not
needed (again, HACKING.rst suggests the try clause should be avoided
too letting the original exception to flow).

Change-Id: Ief779bada1aa53837d62e3f58a7d3418eef494ba
Implements: blueprint replace-self-fail
Merge "removes self.fail as suggested by HACKING.rst"