chroot: make the resource limits name map module-global
chroot: make the resource limits name map module-global

Move the resource limits name map out of the setRlimits() function, and
use it to set up a reverse of the same map in init().

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>

Closes: #891
Approved by: rhatdan

projectatomic/buildah,projectatomic/buildah,TomSweeneyRedHat/buildah,rhatdan/buildah,projectatomic/buildah,nalind/buildah-1,ipbabble/buildah,TomSweeneyRedHat/buildah,nalind/buildah-1,rhatdan/buildah,ipbabble/buildah,nalind/buildah,nalind/buildah,nalind/buildah-1,TomSweeneyRedHat/buildah,rhatdan/buildah