Format error by value

- Use `%v` verb to format errors.
- Give `param` constant in portallocator some better name.

Signed-off-by: Michal Minar <miminar@redhat.com>

api/common.go

@@ -104,7 +104,7 @@ func FormGroup(key string, start, last int) string {
 func MatchesContentType(contentType, expectedType string) bool {
 	mimetype, _, err := mime.ParseMediaType(contentType)
 	if err != nil {
-		log.Errorf("Error parsing media type: %s error: %s", contentType, err.Error())
+		log.Errorf("Error parsing media type: %s error: %v", contentType, err)
 	}
 	return err == nil && mimetype == expectedType
 }