nvme: Fix --force flag inversion

nvme: Fix --force flag inversion

argparse sets the default_value member when the argument has been
provided by the user. But in parse_and_open we set O_EXCL when --force
is not used.

It also introduced a regression in the 'id-ns' where the --force flag
is used to determine which function is used to identify the
namespace (nvme_identify_allocated_ns() vs nvme_identify_ns()).

Fixes: 2100609 ("nvme: open namespace exclusive by default")
Signed-off-by: Daniel Wagner <dwagner@suse.de>