Correct False Positive on Offline Test

Correct False Positive on Offline Test

Now that we have filenames with hashes in them
the likelyhood of finding the numbers 4, 0, and 4
not as an http status are much higher, leading to
a false negative on tests that look at the http
status code. Looking for the string ' 404 ' narrows
the search to actual 404 errors (at least until we
have a file that's exactly 404 bytes long in the
offline interface).

Signed-off-by: Jason Boyer <JBoyer@library.in.gov>