Revert "nss: avoid to use the hardcode kernel version"

This reverts commit 4c80c557508e088fe226bfa1834464b505404652.

We *cannot* have nss becoming machine specific, that makes no sense.
lib/oe/rootfs.py: fix RPM multilib issue

For some odd reason (at least I couldn't find an explanation to this,
yet), if a multilib version of a package is installed after the main one
(that is: in a different smart session), the main package binaries are
not overwritten.

This commit restores the functionality to the original one, before
migrating to python: feed all the packages to smart, apart from attempt
only ones which are installed separately.

Signed-off-by: Laurentiu Palcu <laurentiu.palcu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>