common/rc: explicitly test for engine availability in _require_fio

common/rc: explicitly test for engine availability in _require_fio

The current test in _require_fio (--warnings-fatal --showcmd) does not
fail if an invalid/unavailable io engine is specified.

Add an explicit test that every requested io engine in the job file
is actually available.

Also, remove the "ioe_e4defrag" entries in the [global] stanza of several
ext4 tests which use fio jobfiles. While ioengines can be set in the
[global] section, they can also be overridden in individual, subsequent
stanzas. In each affected test (ext4/301, ext4/302, ext4/303, and
ext4/304) every individual stanza after [global]re-specifies an ioengine;
either with ioengine=e4defrag or ioengine=libaio.

Because of this re-specification, the ioengine in the [global] section
is ignored. This is a good thing, because ioe_e4defrag is not a valid
ioengine, and would fail this new hand-rolled check, even though fio
did not complain.

So rather than over-complicate this new check, simply remove the unused,
invalid "ioengine=ioe_e4defrag" lines in these tests.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>