Wrong handling of Entity::save() return value

[pfrenssen]

Currently the entity form code that is generated thinks that the return value of Entity::save() is a boolean indicating success or failure, but this is not correct. This probably changed at some point in the past.

In current HEAD if a failure occurs during the saving of the entity an exception is thrown. Instead of a boolean, this method returns either SAVED_NEW or SAVED_UPDATED. We can use this information to provide a more fitting message.

[pfrenssen]

Here is the relevant documentation from EntityInterface:

  /**
   * Saves an entity permanently.
   *
   * When saving existing entities, the entity is assumed to be complete,
   * partial updates of entities are not supported.
   *
   * @return int
   *   Either SAVED_NEW or SAVED_UPDATED, depending on the operation performed.
   *
   * @throws \Drupal\Core\Entity\EntityStorageException
   *   In case of failures an exception is thrown.
   */
  public function save();

[jmolivas]

@pfrenssen: Thanks for the PR