test/nvmf: Don't inherit last exit status from errexit

If return is called without specifying the exit status while being
used in the trap context, it inherits the exit status code from the
last cmd that triggered the errexit (i.e. the cmd which was run right
before the trap). In this particular case it may be quite unexpected
since return is called after successful execution of the modprobe,
implying the overal success of the function. However, as set -e is
called right before return, the function returns with a != 0.

To avoid this behavior, explicitly return from the function with 0.

Change-Id: I8b21e7aa6cd5628f14b66e559d05b4d0a20e2050
Signed-off-by: Michal Berger <michalx.berger@intel.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/1807


Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Community-CI: Broadcom CI
Reviewed-by: Maciej Szwed <maciej.szwed@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>