.tools: make GetFetchHeadCommit do what it says
.tools: make GetFetchHeadCommit do what it says

Signed-off-by: Jonathan Boulle <0d47477beef1d882e8812885f3dcf66c4a47c346@gmail.com>

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