Improve error message when syncing a project with invalid groups.
Improve error message when syncing a project with invalid groups.

Change-Id: Iaf5c2a0f00667dc09bcf455cfe2f39bfbaa2bfc0

testbetta/repo-pub,couchbasedeps/git-repo,codetutil/git-repo,couchbasedeps/git-repo,GatorQue/git-repo-flow,gbraad/git-repo,slfyusufu/repo,testbetta/repo-pub,mozilla/git-repo,biaolv/git-repo,FuangCao/git-repo,xyyangkun/git-repo,simbasailor/git-repo,biaolv/git-repo,GatorQue/git-repo-flow,testbetta/git-repo-pub,chenzilin/git-repo,dodocat/git-repo,mozilla/git-repo,kdavis-mozilla/repo-repo,nuclearmistake/repo,GerritCodeReview/git-repo,xyyangkun/git-repo,iAlios/git-repo,frogbywyplay/git-repo,ediTLJ/git-repo,ronan22/repo,codetutil/git-repo,slfyusufu/repo,iAlios/git-repo,CyanogenMod/tools_repo,zemug/repo,qioixiy/git-repo,chzhong/git-repo,FuangCao/repo,frogbywyplay/git-repo,petemoore/git-repo,jingyu/git-repo,chzhong/git-repo,CyanogenMod/tools_repo,FlymeOS/repo,mer-tools/git-repo,petemoore/git-repo,kdavis-mozilla/repo-repo,testbetta/git-repo-pub,FuangCao/git-repo,mixedpuppy/git-repo,FuangCao/repo,gabbayo/git-repo,qioixiy/git-repo,4455jkjh/repo,lewixliu/git-repo,lipro-yocto/git-repo,4455jkjh/repo,FlymeOS/repo,nuclearmistake/repo,11NJ/git-repo,simbasailor/git-repo,gabbayo/git-repo,gbraad/git-repo,GerritCodeReview/git-repo,jingyu/git-repo,chenzilin/git-repo,zemug/repo,mixedpuppy/git-repo,aosp-mirror/tools_repo,ediTLJ/git-repo,ronan22/repo,TheQtCompany/git-repo,darrengarvey/git-repo,mer-tools/git-repo,aosp-mirror/tools_repo,11NJ/git-repo,lipro-yocto/git-repo,darrengarvey/git-repo,dodocat/git-repo,wavecomp/git-repo,wavecomp/git-repo,lewixliu/git-repo,TheQtCompany/git-repo