Support the AWS_REGION env var

[tirsen]

What problem does this PR solve?

Only override the region if it has been explicitly set, otherwise we clobber the standard AWS_REGION env var

pingcap/dumpling#155 (comment)

What is changed and how it works?

Support the standard AWS_REGION env var

Check List

Tests

• Manual test (add detailed scripts or steps below)

Release notes

• Region no longer automatically defaults to us-east-1, it uses the AWS_REGION env var if specified

[kennytm]

please add a test case to s3_test.go (extending TestApplyUpdate should be good)

rest LGTM

[tirsen]

Ah yes I removed the hard coded us-east-1 and updated the tests. This somewhat breaks backwards compatibility though but probably not in a bad way. Hardcoding us-east-1 could be disastrous.

[kennytm]

i think we need a

if len(aws.StringValue(ses.Config.Region)) == 0 {
    ses.Config.Region = aws.String("please supply --s3.region")
}

after line 250 to prevent that MissingRegion error thrown by the AWS SDK.

[ti-chi-bot]

@tirsen: PR needs rebase.

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