HOWTO: use proper (or drop wrong usage of) option type =bool

There are options whose .type field are FIO_OPT_BOOL, but not using
=bool for arg type. Likewise there are options whose .type field
are not FIO_OPT_BOOL, but using =bool for arg type.

The options without explicit arg types in HOWTO seem to be for
FIO_OPT_STR_SET, which is not the same as FIO_OPT_BOOL.

The man page also has these, but not the same as the ones in HOWTO.
Also fix a typo "(mtd)skipbad=bool" in the man page which should be
"(mtd)skip_bad=bool".

Signed-off-by: Tomohiro Kusumi <tkusumi@tuxera.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>