wcst_import - check if credentials are needed

[Bang Pham Huu]

If wcst_import doesn't have credentials and petascope is enabled with authentication then, petascope throws the error to wcst_import:

<ows:ExceptionText>Missing basic authentication header with username:password encoded in Base64 string from request</ows:ExceptionText>

In this case, wcst_import can detect the HTTP code 403 and write that it needs credentials provided (e.g: with -i).