fio: allow general repeatability

This patch adds a "allrandrepeat" option similar to the existing
randrepeat.  But other than the former option it does not only affect
the random I/O pattern, but also all remaining users of randomness as
well.

By that e.g. testcases using nrfiles, filesize ranges, blocksizesplit
ranges and so on will stay repeatable across (euqally parametrized) runs
as well.  To maintain compatibility the default is off.

Signed-off-by: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
Update by me to fix missing thread_options.h and cconv.c change.

Signed-off-by: Jens Axboe <axboe@fb.com>