Return golang compliant names for UID and GID in User
Return golang compliant names for UID and GID in User

Signed-off-by: Alexander Morozov <4efb7da3e38416208b41d8021a942884d8a9435c@docker.com>

jonboulle/specs,opencontainers/specs,vishh/specs,hqhq/runtime-spec,opencontainers/runtime-spec,gao-feng/specs,mheon/specs,marcosnils/specs,hqhq/specs,ChengTiesheng/specs,ujuc/specs,laijs/specs,runcom/specs,talwai/specs,wking/opencontainer-specs,wangkirin/specs,vbatts/specs,wking/opencontainer-runtime-spec,zenlinTechnofreak/specs,HardikDR/specs,cloudfoundry-incubator/specs