runtests: clean up code in runtests.sh

Use uppercase for global and lowecase for local valiable consistently.
Don't use single letter variable names and add some comments.

No functional changes.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
1 file changed