If no secret key is available, don't try to use cache

If no secret key is available, don't try to use cache

In the unlikely event that no secret key is available, we shouldn't
rely on the cache at all in TemplateParser.

Adding new compileForEval() function and and moving eval() outside
of if statement to prevent code duplication.

Also, if the template fails integrity check, generate a notice
instead of throwing an exception in case we change the secret key.

Change-Id: Id44fdcc9533fc8a9c77e84fcebaa064f602477c6