Allow overriding etcd version in tests

... so that we can try multiple etcd versions more easily.

Change-Id: I254186c052590af804931ab2e37f6a11129f06b6
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>

setup-etcd-env.sh

@@ -1,7 +1,7 @@
 #!/bin/bash
 set -eux
 if [ -z "$(which etcd)" ]; then
-    ETCD_VERSION=3.4.27
+    ETCD_VERSION=${ETCD_VERSION:-3.4.27}
     case `uname -s` in
         Darwin)
             OS=darwin

tox.ini

@@ -27,6 +27,8 @@ commands =
 allowlist_externals =
   find
   ./setup-etcd-env.sh
+passenv =
+  ETCD_VERSION
 
 [testenv:update-states]
 deps =