merge branch 'pr-1816'
merge branch 'pr-1816'

  runc: not require uid/gid mappings if euid()==0

LGTMs: 1ab352e9314c20d760dd168a2a849d6ab6d15b05@cyphar
Closes #1816

dqminh/runc,laijs/runc,laijs/runc,estesp/runc,cyphar/runc,adrianreber/runc,mYmNeo/runc,opencontainers/runc,justincormack/runc,kolyshkin/runc,crosbymichael/runc,mheon/runc,kolyshkin/runc,crosbymichael/runc,xiaochenshen/runc,rhatdan/runc,mYmNeo/runc,opencontainers/runc,kolyshkin/runc,dqminh/runc,cyphar/runc,opencontainers/runc,dqminh/runc,adrianreber/runc,rhatdan/runc,opencontainers/runc,estesp/runc,xiaochenshen/runc,justincormack/runc,cyphar/runc,mheon/runc,mikebrow/runc,mYmNeo/runc,mheon/runc,kolyshkin/runc,crosbymichael/runc,dqminh/runc,estesp/runc,laijs/runc,rhatdan/runc,xiaochenshen/runc,mikebrow/runc,adrianreber/runc,justincormack/runc,rhatdan/runc,mikebrow/runc