This commit moves much of the platform-specific logic from the
reverse_http handler down into the payloads. This makes the handler
a bit more agnostic of what the payload is (which is a good thing).
There is more to do here though, and things can be improved.
Handling of datastore settings has been changed to make room for the
ability to override the datastore completely when generating the
payloads. If a datastore is given via the `opts` then this is used
instead otherwise it falls back to the settings specified in the usual
datatstore location.
Down the track, we'll have a payload that supports multiple stages, and
the datastore will be generated on the fly, along with the stage itself.
Without this work, there's no other nice way of getting datastore
settings to be contained per-stager.
Calling .new on payload modules does not perform parameter validation, leading
to a number cached sizes based on invalid parameters. Most notably,
normalization does not occur either, which makes all OptBool params default to
true.
See the complaint on #4039. This doesn't fix that particular
issue (it's somewhat unrelated), but does solve around
a file parsing problem reported by @void-in
bwatters-r7