A+C: add Mrunal Patel (Red Hat corporate CLA)

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://codereview.appspot.com/152010043
syscall: support UID/GID map files for Linux user namespaces

Fixes issue 8447.

LGTM=iant
R=golang-codereviews, bradfitz, iant
CC=golang-codereviews
https://codereview.appspot.com/126190043

Committer: Ian Lance Taylor <iant@golang.org>