generic/079,277: require chattr, not xattrs

generic/079,277: require chattr, not xattrs

Add a new helper, _require_chattr, which allows the test to explicitly
check to see if the file system supports a specific chattr flag, as
not all file systems support chattr +A or chattr +i, and the presence
of extended attribute support is has nothing to do with a specific
chattr flag being supported.

Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>