tests/Dockerfile: update import path to "go.etcd.io/etcd"
tests/Dockerfile: update import path to "go.etcd.io/etcd"

Signed-off-by: Gyuho Lee <0fbd30d364d71722b926950b451cecd97b54fc29@amazon.com>

ajityagaty/etcd,cockroachdb/etcd,coreos/etcd,cockroachdb/etcd,dannysauer/etcd,mqliang/etcd,rnaveiras/etcd,xiang90/etcd,ajityagaty/etcd,ajityagaty/etcd,rnaveiras/etcd,gyuho/etcd,etcd-io/etcd,mqliang/etcd,li-ang/etcd,mkumatag/etcd,mkumatag/etcd,li-ang/etcd,coreos/etcd,vimalk78/etcd,gyuho/etcd,vimalk78/etcd,etcd-io/etcd,mkumatag/etcd,mqliang/etcd,joshix/etcd,rnaveiras/etcd,xiang90/etcd,dannysauer/etcd,etcd-io/etcd,joshix/etcd