Add support for filtering on region

[kadaan]

Add support for filtering on region so that I can have one config file that can work across multiple regions.

[jckuester]

Not sure if something is missing here. I think also the initAwsProvider(*profile, *region, *maxRetries) has to be also specifically initialized for the region one wants to work with (https://github.com/cloudetc/awsweeper/pull/50/files#diff-c4de833e2982802ae3a842e94963b5c7R69).

We probably need to add an integration test for this too, so that we can the issue I mentioned. I can provide a test if I find time

[kadaan]

This is simply about exposing the region specified on the cli as part of the resources, so that it can be filtered on. This allows me to write a config that I can use in different regions and will perform differently.

[kadaan]

@jckuester This should be resurrected. The whole concept of this still works in the re-write you have done. It enables you to write a cleanup specification like:

aws_instance:
  - region: NOT(us-east-1)
    tags:
      Name: my-server-\d+-.+
    created:
      before: 1h
  - region: us-east-1
    tags:
      Name: my-server-0[^1]-.+
    created:
      before: 1h

[jckuester]

@kadaan I picked the code from your branches (hope that is OK) and added some tests: #137. Lets get the region filter feature merged first and the let's focus on the optimisation for discovery that you provided in a second step.

[kadaan]

@jckuester Sounds great! I'd love to know if the perf improvements seem good to you. For me they were a really big help when trying to cleanup resources in 13+ regions.