nvmetcli: Install nvmetcli in /usr/sbin with setup.py

According to the README, one can install nvmetcli through setup.py.
When one tries this though, the nvmetcli isn't configured in system's
$PATH.

Adding nvmetcli to scripts argument in setup call does half of the job.
Then, in order to install it in the correct location in a maintanable
way it's introduced setup.cfg file which contains 'install_scripts'
parameter for 'install' command set to /usr/sbin.

Nothing changes on the .deb package creation, the .rpm package process
in the other hand was made simpler by lines that are now done by
setup.py + setup.cfg settings.

Signed-off-by: Mauro S. M. Rodrigues <maurosr@linux.vnet.ibm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>