fstests: skip AIO-related tests when CONFIG_AIO=n

When running xfstests on a kernel configured with CONFIG_AIO=n, all
AIO-related tests fail, often due to an error similar to the

    error Function not implemented during io_setup

This affected at least the following tests: generic/036,
generic/112, generic/113, generic/198, generic/207, generic/208,
generic/210, generic/211, generic/239, generic/323, generic/427,
xfs/240, xfs/241.

Fix this by enhancing the 'feature' program to allow testing for
asynchronous I/O support, then skipping all AIO-related tests when
AIO is unsupported.

This change is useful because CONFIG_AIO is sometimes disabled to
reduce the kernel's attack surface (e.g. see

Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>
7 files changed