Support bootstrapping and wiping AWS Credentials

[RobertSzkutak]

Issue #581

[dmcassel]

@RobertSzkutak I just ran a test with a non-AWS configuration and it failed.

ERROR: XDMP-AS: (err:XPTY0004) sec:credentials-set-aws($accessKey, $secretKey) -- Invalid coercion: fn:QName("","secretKey") as xs:string

The implementation of setup:create-credentials and setup:wipe-credentials needs to account for $import-config/sec:credentials not being present. If that's the case, the function should do nothing.

[RobertSzkutak]

Thanks, should be fixed now!

[dmcassel]

Looks good. I've tested that this works fine with non-AWS configuration. I don't have an AWS setup handy, but your code looks good to me.