build: make podman_build a function (#121)

setup.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+
+set -e
+
+podman=`which podman || true`
+
+if [ -z "$podman" ]; then
+  echo "podman needs to be in PATH for this script to work."
+  exit 1
+fi