aws/session: Correct credentials error messages, if not creds founds
aws/session: Correct credentials error messages, if not creds founds

The Shared Config update expanded how the SDK can be configured to load
credentials, but the error message returned when no credentials were
found was not updated to be consistent with current chain provider
message.

calgaryscientific/aws-sdk-go,myshen/aws-sdk-go,calgaryscientific/aws-sdk-go,myshen/aws-sdk-go,yxd-hde/aws-sdk-go,myshen/aws-sdk-go,zmarois/aws-sdk-go,radeksimko/aws-sdk-go,jasdel/aws-sdk-go,xibz/aws-sdk-go,radeksimko/aws-sdk-go,agworld/aws-sdk-go,calgaryscientific/aws-sdk-go,xibz/aws-sdk-go,aws/aws-sdk-go,yxd-hde/aws-sdk-go,zmarois/aws-sdk-go,agworld/aws-sdk-go,xibz/aws-sdk-go,myshen/aws-sdk-go,agworld/aws-sdk-go,zmarois/aws-sdk-go,xibz/aws-sdk-go,yxd-hde/aws-sdk-go,agworld/aws-sdk-go,radeksimko/aws-sdk-go,zmarois/aws-sdk-go,yxd-hde/aws-sdk-go,calgaryscientific/aws-sdk-go,radeksimko/aws-sdk-go