Move Storage Policy validation from parser to class

Currently we validate Storage Policy conflicts while parsing
swift.conf in parse_storage_policies. This let's us get away
with unnatural things in tests like patch_policies with two
policies that have the same name.

Additionally this change makes the rules a bit easier to
identify and assure coverage.

Change-Id: I6cd48e5a3b3658e106ecd20df0b04fd804c028a4
Implements: blueprint storage-policies
Merge "Move Storage Policy validation from parser to class" into feature/ec