Increase random bytes in corrupt file test

Increased the number of random bytes in the test for how the code
handles corrupt folder index files.  The previous test could fail to
throw an exception on occasion.  Increasing the number of bytes from 32
to 128 might do the trick.
Update tests files with non-null offsets

The previous test files all had offsets that were zero (0).  This was
due to a bug that was fixed in commit f372d56.  This commit will replace
all measurement files with a new set that has an offset value of two (2)
hours.

I also created only six files instead of 14, which makes them easier to
deal with.