Make all secrets case insensitive by formatting them to uppercase (#470)

* Uppercase secrets, print error when secret with same name already exists

* Test lower-to-upper case formatting for secrets

pkg/runner/expression.go

@@ -61,6 +61,9 @@ type expressionEvaluator struct {
 }
 
 func (ee *expressionEvaluator) Evaluate(in string) (string, bool, error) {
+	if strings.HasPrefix(in, `secrets.`){
+		in = `secrets.`+strings.ToUpper(strings.SplitN(in, `.`, 2)[1])
+	}
 	re := ee.Rewrite(in)
 	if re != in {
 		log.Debugf("Evaluating '%s' instead of '%s'", re, in)