WIP: Fix regions filtering overriding for each account

[yevgenypats]

• Closes Disabled regions detection is using hardcoded region "us-east-1" that could be a disabled region in some configurations #242
• Related Support Wildcard for Region #391
• Added integration tests as described here

This is a continuation of #391.

As uncovered in #391 this line of detecting which regions are enabled in a specific account is overriding all the accounts. Moreover we don't need the regions field on the client level as this is incorrect and it should be only specified on the account level (even though we can have in the config).

Also, as noted in this comment by @bbernays we don't need the list of regions at all, this also remove the burden of maintaining it.

I'll test it manually but also I think we might need some additional testing here as it's a bit hard to verify manually all the edge-cases.

[yevgenypats]

Closing - Fixed in #391