python-common: reformat ServiceSpec class level service type lists

python-common: reformat ServiceSpec class level service type lists

Reformat the ServiceSpec classes properties KNOWN_SERVICE_TYPES and
REQUIRES_SERVICE_ID. These were previously strings that were converted
to lists via a call to split. With a string there's very little a human
or a tool can do to validate the content. Changing these into proper
lists in the source code brings clarity of intent and the ability to
analyze the code. Because there's no semantic difference what services
are listed where (this means the type could probably be a set - a quest
for another day) I also took the opportunity to sort the contents of the
lists and add some basic comments for what these lists are for.

It also removes the use of (ugly, IMO) line continuations. The downside
is that it makes more total lines, but if that bugs you - use code
folding :-).

Signed-off-by: John Mulligan <jmulligan@redhat.com>