Add specific error message for when accessing a certificate file fails

[rolson]

A PR was merged that fixed an issue with importing a certificate. However we need to follow up on that and make sure to have specific error message for the failure to access a certificate file.

[rolson]

cc @carl8382

[rolson]

It might be useful to have a toolkit level specific error:

enum CertificateError: Error {
    case couldNotAccessSecureScopedResource
    case importError(CertificateImportError)
    case unknown
}

extension CertificateError {
    var message: String {
        switch self {
        case .couldNotAccessSecureScopedResource:
            return "Could not access certificate file."
        case .unknown:
            return "Unknown error accessing and importing the certificate."
        case .importError(let certificateImportError):
            switch certificateImportError {
            case .invalidData:
                return "The certificate file was invalid."
            case .invalidPassword:
                return "The password was invalid."
            default:
                return defaultMessage
            }
        }
    }
}

and use that instead of CertificateImportError

[dfeinzimer]

Completed