.travis: fix issue that etcd exited on Arm64
.travis: fix issue that etcd exited on Arm64

Set env variables ETCD_UNSUPPORTED_ARCH=$(GOARCH)

Signed-off-by: Jianlin Lv <752eae91a476c3d35f9a7fd15fcd40979a048de4@arm.com>

michi-covalent/cilium,michi-covalent/cilium,tklauser/cilium,cilium/cilium,michi-covalent/cilium,tgraf/cilium,tklauser/cilium,cilium/cilium,tklauser/cilium,tklauser/cilium,cilium/cilium,tgraf/cilium,michi-covalent/cilium,cilium-team/cilium,tgraf/cilium,cilium/cilium,michi-covalent/cilium,tgraf/cilium,tgraf/cilium,tgraf/cilium,tklauser/cilium,cilium-team/cilium,cilium/cilium