Fix a couple of issues with system_server forking.

- Remove the obsolete --runtime-init arg. its prescence
  was preventing other arguments from being parsed.

- Be stricter about unparsed args - throw if we see arguments
  we don't expect. This was already implemented but broken
  (probably implemented by a crap programmer).

bug: 19378905
Change-Id: Id8b6158db7ef6368dd13ae61f591cdf2b278dfd1