generic: test immutable attribute efficacy

New tests to make sure that files marked immutable cannot be changed in
any way as soon as the flag is set, except for removing the flag.
generic: check that we can't modify immutable files

Make sure that we can't modify an immutable file regardless of whether
the fd was opened before or after the file became immutable.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
10 files changed