This test used to have fixed-sized arrays for the mounts that it was
checking. However, we periodically run across machines with more
mounts than can fit into those fixed-size arrays. Rather than
periodically increasing the size of those arrays (after re-discovering
that the error is due to fixed-size arrays), just count how many
entries there are and make arrays that are big enough.
Additionally, add a check to ensure that we don't go over the max size
of the array when reading/filling them.
Signed-off-by: Jeff Squyres <jsquyres@cisco.com>