gitignore: ignore test files in "vendor"
gitignore: ignore test files in "vendor"

Signed-off-by: Gyuho Lee <3454051ee3341eb69bdf6fca40899cdad4d86496@gmail.com>

xiang90/etcd,etcd-io/etcd,etcd-io/etcd,li-ang/etcd,sinsharat/etcd,mkumatag/etcd,coreos/etcd,mqliang/etcd,lorneli/etcd,etcd-io/etcd,li-ang/etcd,mqliang/etcd,sinsharat/etcd,joshix/etcd,rnaveiras/etcd,heyitsanthony/etcd,cockroachdb/etcd,bdarnell/etcd,vimalk78/etcd,rnaveiras/etcd,gyuho/etcd,lorneli/etcd,mkumatag/etcd,fanminshi/etcd,ajityagaty/etcd,vimalk78/etcd,heyitsanthony/etcd,xiang90/etcd,whuwxl/etcd,glevand/coreos--etcd,bdarnell/etcd,gyuho/etcd,dannysauer/etcd,mkumatag/etcd,coreos/etcd,rnaveiras/etcd,fanminshi/etcd,joshix/etcd,ajityagaty/etcd,whuwxl/etcd,sebrandon1/etcd,mqliang/etcd,glevand/coreos--etcd,dannysauer/etcd,ajityagaty/etcd,cockroachdb/etcd,sebrandon1/etcd