NVMe unit tests

[Jim Harris]

Hi,

I have a CUnit-based infrastructure with quite a few unit tests for the
FreeBSD nvme driver.  It enables testing a number of corner cases within
the driver without requiring real hardware and stubbing kernel behavior in
some cases to induce the corner cases.  Which leads me to a few questions:

1) Is there interest here in having this pushed into HEAD?  Or would a user
branch be more appropriate?
2) Where in the tree should I put it?  In our internal repo, I have it
under tools/regression/nvme, but maybe sys/dev/nvme/tests is more
appropriate?

Feedback is welcome.

Thanks,

-Jim