Add a simple cli-based test infrastructure with a few tests
to prepare future code changes.
Note that these cannot be run on Travis CI as it does not support
FUSE.
Expected output:
$ tests/run.sh
1 Running unit tests: OK
*** running test_corruption.sh
2 Reading file: OK
3 Reading corrupted file: OK
4 Reading file with MAC: OK
5 Corruption with MAC returns IO error: OK
*** running test_file_expansion.sh
6 Creating files of different sizes: : OK
7 Growing file: OK
8 Internal modification: OK
*** All tests OK
