generic: clean up tests using fio

generic: clean up tests using fio

During the code review for a test to exercises AIO/DIO into unwritten
space, a number of changes were requested that were also applicable to
generic/299 and generic/300 (from which the aforementioned test was
patterned).  For example, the use of run_check, which is deprecated,
was dropped.  In addition, we now rely on the test runner to unmount
the scratch file system.

Also fix a nit I found in generic/095, which resulted in debugging
information in the $seqres.full to get lost when "fio ...
--output=$seqres.full" is run.

[Eryu: add _require_aio to generic/095, fix more indention issues]

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>