Avoid need for workarounds for $AWS_DEFAULT_REGION

[mikljohansson]

The awsudo and awscli tools sets $AWS_DEFAULT_REGION instead of $AWS_REGION as the AWS Golang SDK expected. To use secretary together with awsudo some workarounds are needed, like running a bash subshell and explicitly overriding $AWS_REGION.

• Updated to latest release of AWS golang SDK which supports "Shared Config" (e.g. ~/.aws/config)
• Force enable Shared Config which enables the SDK to read $AWS_DEFAULT_REGION
• Use EC2 meta-data service to autodetect current AWS region if needed (only works inside EC2)

[codecov-io]

Current coverage is 52.17% (diff: 0.00%)

Merging #14 into master will decrease coverage by 3.04%

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