Add /run/nss to LD_LIBRARY_PATH

This fixes issues with glibc-binaries (getent for example) that can't
find NSS modules that are not distributed with glibc.

See this discussion:
http://comments.gmane.org/gmane.linux.distributions.nixos/9940
Merge pull request #116 from rickynils/nss

Add /run/nss to LD_LIBRARY_PATH