etcdmain: Don't print flags when flag parse error
etcdmain: Don't print flags when flag parse error

At present it prints the whole usage and flags, which cause the exact
error message is hidden two screens above.

Fixes #3141

Signed-off-by: Guohua Ouyang <0d3bb08da5ea424b7b8a814403b2239605f8709c@redhat.com>

improbable-io/etcd,heyitsanthony/etcd,delkyd/etcd,SivagnanamCiena/etcd,junxu/etcd,joshix/etcd,vimalk78/etcd,sebschrader/etcd,insionng/etcd,elimisteve/etcd,devfreesg/etcd,jefby/etcd,HideoYamauchi/etcd,cognusion/etcd,steveeJ/etcd,steveeJ/etcd,zaphod-concur/etcd,fasaxc/etcd,hroyrh/etcd,cchamplin/etcd,jravetch/etcd,wowsoso/etcd,onlyjob/etcd,Eagle-X/etcd,mitake/etcd,whuwxl/etcd,wantonsolutions/dinv-etcd,lorneli/etcd,dalanlan/etcd,qqsun8819/etcd,mkumatag/etcd,arthurcolle/etcd,coreos/etcd,mqliang/etcd,YuleiXiao/etcd,wfxiang08/etcd,nekto0n/etcd,chipironcin/etcd,nkhare/etcd,njharman/etcd,westhood/etcd,onlyjob/etcd,siddontang/etcd,jeremyeder/etcd,SivagnanamCiena/etcd,glycerine/etcd,snailwalker/etcd,lzbgt/etcd,mickep76/etcd,mqliang/etcd,plasticbox/etcd,luxas/etcd,li-ang/etcd,betawaffle/etcd,offscale/etcd,insequent/etcd,hongbinz/etcd,openedbox/etcd,swingbach/etcd,sinsharat/etcd,rnaveiras/etcd,elimisteve/etcd,tangkun75/etcd,tguangch/etcd,honeyqa/etcd,msanterre/etcd,sebrandon1/etcd,handsomesun/etcd,a-robinson/etcd,joshix/etcd,lorneli/etcd,glevand/coreos--etcd,shawnps/etcd,kkaneda/etcd,msanterre/etcd,kingland/etcd,akauppi/etcd,axingblog/etcd,TheHippo/etcd,purpleidea/etcd,etcd-io/etcd,Eagle-X/etcd,shawnps/etcd,yichengq/etcd,Yhgenomics/etcd,dnaeon/etcd,njucslqq/etcd,a-robinson/etcd,tangkun75/etcd,giantswarm/etcd,whuwxl/etcd,ajityagaty/etcd,fasaxc/etcd,fgbreel/etcd,raoofm/etcd,CrazyJvm/etcd,xychu/etcd,oscarrr110/etcd,wantonsolutions/dinv-etcd,polvi/etcd,qqsun8819/etcd,glevand/coreos--etcd,chenbaihu/etcd,sayden/etcd,beni55/etcd,svdata/etcd,cockroachdb/etcd,glycerine/etcd,purpleidea/etcd,visheshnp/etcd,beni55/etcd,sofuture/etcd,plasticbox/etcd,fanminshi/etcd,StorReduce/etcd,dannysauer/etcd,gyuho/etcd,endocode/etcd,raoofm/etcd,rnaveiras/etcd,es-chow/etcd,tguangch/etcd,westhood/etcd,CrazyJvm/etcd,Yhgenomics/etcd,bdarnell/etcd,offscale/etcd,visheshnp/etcd,asim/etcd,jonboulle/etcd,mitake/etcd,jonboulle/etcd,etcd-io/etcd,armstrongli/etcd,buaazp/etcd,princeqjzh/etcd,sofuture/etcd,cchamplin/etcd,akauppi/etcd,openedbox/etcd,bdarnell/etcd,sebrandon1/etcd,mkumatag/etcd,rnaveiras/etcd,linuxcer/etcd,xdlinear/etcd,heyitsanthony/etcd,Timer/etcd,Winslett/etcd,freeloop1114/etcd,pauldallen/etcd,sebschrader/etcd,fgbreel/etcd,gouyang/etcd,insequent/etcd,xiang90/etcd,mickep76/etcd,tamird/etcd,jchauncey/etcd,zaphod-concur/etcd,coreos/etcd,polvi/etcd,kkaneda/etcd,hongbinz/etcd,li-ang/etcd,wowsoso/etcd,yichengq/etcd,cognusion/etcd,mike-lerch/etcd,StorReduce/etcd,mqliang/etcd,sayden/etcd,etcd-io/etcd,fanminshi/etcd,yyljlyy/etcd,combk8s/etcd,axingblog/etcd,jefby/etcd,betawaffle/etcd,iamqizhao/etcd,gouyang/etcd,sinsharat/etcd,dalanlan/etcd,arthurcolle/etcd,TheHippo/etcd,tempbottle/etcd,gae123/etcd,rchicoli/etcd,imzhulei/etcd,siddontang/etcd,Timer/etcd,dannysauer/etcd,luxas/etcd,gyuho/etcd,cockroachdb/etcd,asim/etcd,lumjjb/etcd,giantswarm/etcd,rchicoli/etcd,snailwalker/etcd,lzbgt/etcd,yyljlyy/etcd,bluebreezecf/etcd,achanda/etcd,tempbottle/etcd,tamird/etcd,njharman/etcd,youxidev/etcd,oscarrr110/etcd,spacejam/etcd,achanda/etcd,ktateish/etcd,handsomesun/etcd,ajityagaty/etcd,OyTao/etcd_learning,pauldallen/etcd,ravigadde/etcd,wfxiang08/etcd,wantonsolutions/dinv-etcd,swingbach/etcd,es-chow/etcd,jchauncey/etcd,armstrongli/etcd,njucslqq/etcd,Winslett/etcd,linuxcer/etcd,OyTao/etcd_learning,shakefu/etcd,hongchaodeng/etcd,ajityagaty/etcd,lumjjb/etcd,jlamillan/etcd,ravigadde/etcd,mike-lerch/etcd,spacejam/etcd,fasaxc/etcd,hroyrh/etcd,chenbaihu/etcd,endocode/etcd,xychu/etcd,delkyd/etcd,hongchaodeng/etcd,yudai/etcd,improbable-io/etcd,ktateish/etcd,kingland/etcd,gityf/etcd,yudai/etcd,jravetch/etcd,iamqizhao/etcd,jlamillan/etcd,mkumatag/etcd,jeremyeder/etcd,chipironcin/etcd,combk8s/etcd,shakefu/etcd,HideoYamauchi/etcd,gityf/etcd,dnaeon/etcd,imzhulei/etcd,gae123/etcd,freeloop1114/etcd,devfreesg/etcd,svdata/etcd,bluebreezecf/etcd,junxu/etcd,honeyqa/etcd,nkhare/etcd,YuleiXiao/etcd,nekto0n/etcd,xdlinear/etcd,buaazp/etcd,xiang90/etcd,youxidev/etcd,insionng/etcd,princeqjzh/etcd,vimalk78/etcd