Fail reconciliation when specified Secret does not exist instead of generating it

The following discussion from !83 (merged) should be addressed:

@pursultani started a discussion: (+3 comments)

GetSingle ignores NotFound error and returns nil. This means when the specified Secret is not found then the generates one. This is incorrect.

The standard procedure is that when the Secret reference is not specified then the default Secret is generated. Otherwise it must try and locate the Secret that user has specified and fail to reconcile if it can not be found.

Additionally, we have to fix: