MID-6837: midPoint does NOT start if *_FILE in config.xml is not found

This affects only cases when the key is suffixed with _FILE and the
value is read from the file specified as the element value, e.g.:
<keyStorePassword_FILE>${midpoint.home}/pwd.txt</keyStorePassword_FILE>

repo/system-init/src/main/java/com/evolveum/midpoint/init/StartupConfiguration.java

@@ -285,9 +285,10 @@ private void resolveFileReferences() {
                     LOGGER.trace("Property '{}' was read from '{}': '{}'", valueKey, filename, value);
                 } catch (IOException e) {
                     String message = "Couldn't read the value of configuration key '" + valueKey
-                            + "' from the file '" + filename + "': " + e.getMessage();
+                            + "' from the file '" + filename + "': " + e.toString();
                     LoggingUtils.logUnexpectedException(LOGGER, message, e);
                     System.err.println(message);
+                    throw new SystemException(e);
                 }
             }
         });