wire session factory and partial flyweight optional support

[kapilt]

not sure wrt to approach here, i've tried a separate query executor class against extant meta models as well, which might be a little nicer, but wanted to try and see what it looked like to modify extant for library usage.

This unifies the client creation behind a passed object (session_factory) through most of the tree. cloudwatch usage is made lazy, as client construction does require reading model files and is noticable in lambda. there's partial support for choosing between flyweight resource classes and raw dictionaries.

mostly to start a discussion, i'll post a query branch later this week for comparison.

[kapilt]

wrt to query model, https://github.com/capitalone/cloud-custodian/blob/master/c7n/query.py#L81

that's basically just a base layer reimplementing the query logic embedded in resource.py but also just working with the raw data structs

[avram]

@garnaat Thoughts on this approach vs #86?

[garnaat]

I like this basic approach. I'm going to play around with it a bit this weekend and may have more comments.

[kapilt]

fwiw, i've been expanding out use of skew models to include aws config support. also considering expansion to include create, modify, delete events.

[walterheck]

Any chance this can be amended and merged? Would be really nice to be able to use this..