libcontainer: user: update tests for GetAdditionalGroups
libcontainer: user: update tests for GetAdditionalGroups

Update the tests to use the test-friendly GetAdditionalGroups API,
rather than making random files for no good reason.

Signed-off-by: Aleksa Sarai <b305c9b0212d6145eea67bbffd24e29cb79c759c@cyphar.com>

boucher/runc,chenchun/runc,cxxly/runc,laijs/runc,runcom/runc,mikebrow/runc,carlye566/runc,ChengTiesheng/runc,jhjeong-kr/runc,YujiOshima/runc,calavera/runc,fabiokung/runc,mYmNeo/runc,aidanhs/runc,cyphar/runc,avagin/runc,ChengTiesheng/runc,dieface/runc,intfrr/runc,meihuabo/runc,mikebrow/runc,subuser-security/runc,avagin/runc,cyphar/runc,talwai/runc,mYmNeo/runc,cxxly/runc,xiaochenshen/runc,zenlinTechnofreak/runc,dqminh/runc,HardikDR/runc,rootfs/runc,kolyshkin/runc,nkwilson/runc,wangkirin/runc,keloyang/runc,InformatiQ/runc,mapk0y/runc,booyaa/runc,intfrr/runc,runcom/runc,mheon/runc,zenlinTechnofreak/runc,inatatsu/runc,cloudfoundry-incubator/runc,runcom/runc,clnperez/runc,fabiokung/runc,sunyuan3/runc,meihuabo/runc,estesp/runc,mikebrow/runc,xiaochenshen/runc,laijs/runc,willmtemple/runc,ycaihua/runc,keloyang/runc,ddnbgroup/runc,ddnbgroup/runc,carlye566/runc,dieface/runc,marcosnils/runc,shishir-a412ed/runc,rajasec/runc,adrianreber/runc,sunyuan3/runc,cloudfoundry-incubator/runc,aidanhs/runc,mheon/runc,aidanhs/runc,crosbymichael/runc,hqhq/runc,fabiokung/runc,xiaochenshen/runc,jwuwork/runc,justincormack/runc,WeiZhang555/runc,coolljt0725/runc,wcwxyz/runc,han-wang/runc,marcosnils/runc,navidshaikh/runc,estesp/runc,marcosnils/runc,crosbymichael/runc,wking/runc,gitido/runc,ZJU-SEL/runc,albertoleal/runc,sallyom/runc,markllama/runc,HuKeping/runc,chenchun/runc,jwuwork/runc,hxfeng/runc,boucher/runc,mheon/runc,stefanberger/runc,axsh/runc,jwuwork/runc,nkwilson/runc,kimh/runc,albertoleal/runc,docker/runc,whosthatknocking/runc,liuwharton/runc,kimh/runc,whosthatknocking/runc,crosbymichael/runc,haijunTan/runc,cloudfoundry-incubator/runc,dqminh/runc,wking/runc,estesp/runc,willmtemple/runc,adrianreber/runc,rootfs/runc,maxamillion/runc,InformatiQ/runc,subuser-security/runc,dqminh/runc,jhowardmsft/runc,rajasec/runc,hqhq/runc,WeiZhang555/runc,YujiOshima/runc,inatatsu/runc,maxamillion/runc,shishir-a412ed/runc,han-wang/runc,opencontainers/runc,markllama/runc,HardikDR/runc,balajibr/runc,kimh/runc,sunyuan3/runc,mapk0y/runc,rhatdan/runc,meihuabo/runc,ChengTiesheng/runc,rhatdan/runc,adrianreber/runc,subuser-security/runc,sallyom/runc,kolyshkin/runc,wcwxyz/runc,liuwharton/runc,HardikDR/runc,shishir-a412ed/runc,wcwxyz/runc,willmtemple/runc,jhowardmsft/runc,haijunTan/runc,intfrr/runc,gitido/runc,lizf-os/runc,axsh/runc,YujiOshima/runc,clnperez/runc,lizf-os/runc,HuKeping/runc,dieface/runc,boucher/runc,avagin/runc,balajibr/runc,talwai/runc,booyaa/runc,stefanberger/runc,navidshaikh/runc,laijs/runc,calavera/runc,jhjeong-kr/runc,haijunTan/runc,keloyang/runc,wking/runc,opencontainers/runc,jhowardmsft/runc,wangkirin/runc,whosthatknocking/runc,liuwharton/runc,cxxly/runc,mYmNeo/runc,wangkirin/runc,justincormack/runc,dqminh/runc,abduld/runc,rhatdan/runc,hqhq/runc,ZJU-SEL/runc,booyaa/runc,clnperez/runc,vbatts/runc,InformatiQ/runc,vbatts/runc,ZJU-SEL/runc,abduld/runc,docker/runc,coolljt0725/runc,rajasec/runc,rhatdan/runc,ycaihua/runc,calavera/runc,zenlinTechnofreak/runc,markllama/runc,ycaihua/runc,cyphar/runc,jhjeong-kr/runc,abduld/runc,ddnbgroup/runc,inatatsu/runc,balajibr/runc,ekuric/runc,albertoleal/runc,carlye566/runc,ekuric/runc,kolyshkin/runc,opencontainers/runc,sallyom/runc,opencontainers/runc,chenchun/runc,lizf-os/runc,stefanberger/runc,talwai/runc,hxfeng/runc,mapk0y/runc,coolljt0725/runc,rootfs/runc,han-wang/runc,gitido/runc,maxamillion/runc,HuKeping/runc,docker/runc,kolyshkin/runc,vbatts/runc,axsh/runc,WeiZhang555/runc,hxfeng/runc,nkwilson/runc,justincormack/runc,ekuric/runc,navidshaikh/runc