generic/311: add fallocate() check

generic/311: add fallocate() check

Generic/311 fails when run on a test filesystem that does not
support fallocate().  Its I/O load is produced by fsync-tester,
which uses fallocate() system calls to allocate blocks for some of
its test cases.  This causes EOPNOTSUPP failures when the test is
run on indirect block-mapped ext4 filesystems.

Verify that the test filesystem supports fallocate() before
proceeding with the test, checking for block allocation
capabilities.  Also, fix a minor error message typo.

Signed-off-by: Eric Whitney <enwlinux@gmail.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>