Support colon (:) in profile names

[abrooksv]

This is a feature request from a customer using the JetBrains toolkit (aws/aws-toolkit-jetbrains#1751)

They would like to be able to use a colon in their profile name to match the CLI:

aws s3 ls --profile foo:bar
2020-05-01 14:47:55 ajnbjanbjanbjanbjanbj

[debora-ito]

Marking as a feature request.

[jeffalder]

@abrooksv This is not a difficult PR - I did the last round: #1538