Allow using AWS_PROFILE env variable in combination with ~/.aws/config

[sleepdeprecation]

Similar to #65 and #70, this change allows users to use standard AWS command line flags with unicreds, and have the application read from ~/.aws/config, so that configured profiles are available.

Allows

unicreds list --region us-east-1 -t table -p root_profile -R arn:aws:iam::account_id:role/role_name

to be replaced with

AWS_PROFILE=role_profile unicreds list --region us-east-1 -t table

Assuming that role_profile is configured in ~/.aws/config with

[profile role_profile]
role_arn = arn:aws:iam::account_id:role/role_name
source_profile = root_profile

[sleepdeprecation]

@wolfeidau any thoughts? Is this good to go?

The test failures are because the upstream AWS SDK changed an interface, and the mock no longer fulfills the interface, unrelated to this code.

[wolfeidau]

Heya this is an interesting idea.

I need to do a release to bump and vendor upstream deps so I will do that in the next couple of days, then we can compare notes on this.

[afirth]

be good to update the usage with this PR too. Can confirm the build passes with #78 in as well. https://travis-ci.org/flippa/unicreds/builds/338795559

[afirth]

Also, should this respect the region set in the profile?

$ cat ~/.aws/config
[default]
region = us-east-1

$ unicreds  list
   ⨯ failed                    error=MissingRegion: could not find region configuration

[sleepdeprecation]

@afirth new commit now respects the region set in the profile. Working on usage docs.

[sleepdeprecation]

Usage documentation updated to include using AWS_* env variables and respecting the credentials/config documentation.

[wolfeidau]

If you rebase master I have merged the PR #78 and i will merge.

[sleepdeprecation]

Rebased against master, waiting for CI.

[aerostitch]

Hi, I'd be really interested in this, any word on when it will be merged? Thanks Joseph