etcd: implement separate system tests

- add t13_etcd test directory
- etcd will be started for the unit tests and each system test
- etcd will load fixture DB export if requested by the test
- existing tests are reused for etcd testing

system/t13_etcd/install-etcd.sh

@@ -0,0 +1,12 @@
+#!/bin/sh
+
+# etcd test env
+ETCD_VER=v3.5.2
+DOWNLOAD_URL=https://storage.googleapis.com/etcd
+
+if [ ! -e /tmp/etcd-${ETCD_VER}-linux-amd64.tar.gz ]; then
+    curl -L ${DOWNLOAD_URL}/${ETCD_VER}/etcd-${ETCD_VER}-linux-amd64.tar.gz -o /tmp/etcd-${ETCD_VER}-linux-amd64.tar.gz
+fi
+
+mkdir /srv/etcd
+tar xf /tmp/etcd-${ETCD_VER}-linux-amd64.tar.gz -C /srv/etcd --strip-components=1