lib/codereview: allow addca CLs without LGTM
lib/codereview: allow addca CLs without LGTM

LGTM=gri
R=golang-codereviews, gri
CC=golang-codereviews
https://codereview.appspot.com/61610043

tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme