generic/{436,445}: check falloc support

generic/{436,445}: check falloc support

The sanity test case in those tests (i.e. 13..17)
are all skipped in fs with no falloc support, but the tests
are reported to pass.

For example, from 445.full:

 File system supports the default behavior.
 File system does not support fallocate.
 Allocation size: 4096
 17. Test file with unwritten extents, data-hole-data inside page
 Test skipped as fs doesn't support unwritten extents.

Explicitly check for falloc support before running those tests
so they would be properly reported as skipped.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>