tests/e2e: backport e2e cluster setup

Finish backporting the remaining functions from the original backport
from PR etcd-io#17075.

Backported commit 65add8c

Signed-off-by: Ivan Valdes <ivan@vald.es>

tests/framework/e2e/cluster.go

@@ -491,6 +491,15 @@ func (epc *EtcdProcessCluster) EndpointsV3() []string {
 	return epc.Endpoints(func(ep EtcdProcess) []string { return ep.EndpointsV3() })
 }
 
+func (epc *EtcdProcessCluster) EndpointsGRPC() []string {
+	return epc.Endpoints(func(ep EtcdProcess) []string { return ep.EndpointsGRPC() })
+}
+
+func (epc *EtcdProcessCluster) EndpointsHTTP() []string {
+	return epc.Endpoints(func(ep EtcdProcess) []string { return ep.EndpointsHTTP() })
+}
+
+
 func (epc *EtcdProcessCluster) Endpoints(f func(ep EtcdProcess) []string) (ret []string) {
 	for _, p := range epc.Procs {
 		ret = append(ret, f(p)...)