nvme: drop default subsysnqn argument from _nvme_passthru_target_{setup|cleanup}

nvme: drop default subsysnqn argument from _nvme_passthru_target_{setup|cleanup}

Remove the last positional argument for
_nvme_passthrue_target_{setup|cleanup} which most test pass in the
default subsysnqn anyway. There is little point in cluttering all the
test textual noise.

While at it, also use subsysnqn as variable name everywhere, instead of
subsys_name.

Signed-off-by: Daniel Wagner <dwagner@suse.de>
[Shin'ichiro: dropped the change for _nvme_disconnect_subsys in nvme/037]
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>