Update FileFailureInject module

I implemented two changes here:
* I renamed fopenFail() to fopenSetReturn() since this better
  represents how it is actually used in the tests for this project.  It
  isn't just used to fail the fopen() call (by returning NULL), it is
  also used to return a dummy non-NULL value so that code under test
  will think that the fopen was successful.  Future I/O calls will
  also go to mocks so that the dummy FILE pointer is ignored.
* Added a fcloseIgnore() API which can hook fclose() calls to ignore
  the dummy FILE* that is returned from fopen() during testing.

These two changes allow the code under test to think that is processing
FILE data when all of the test data is actually coming from memory via
mocks.