bump(sys-libs/glibc): Pull in 2.17, remove some configs from /etc

One oddity here: /etc/nsswitch.conf is setup as a postinst command in
order to avoid conflicting with baselayout once it starts installing
nsswitch.conf instead. Later glibc won't provide nsswitch.conf at all.
Merge pull request #341 from marineam/glibc

bump(sys-libs/glibc): Pull in 2.17, remove some configs from /etc