fstests: add missing checks of fallocate feature

fstests: add missing checks of fallocate feature

Many test cases use xfs_io -c 'falloc' but forgot to add
_require_xfs_io_command "falloc". This will fail the test case if we
run the test case on a file system without fallcoate support e.g.
F2FS.

While we believe that normal fallocate(mode = 0) is always supported
on Linux, it is not true. Fallocate is disabled in several
implementations of zoned block support for file systems because the
pre-allocated region will break the sequential writing rule.

Currently, several test cases unconditionally call fallocate().
Let's add _require_xfs_io_command "falloc" to properly check the
feature is supported by a testing file system.

Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>