build: implement a framework for starting test servers during tests

Test servers are implemented by docker containers and run real servers
for rclone to test against.

fstest/testserver/init.d/docker.bash

@@ -0,0 +1,22 @@
+#!/bin/bash
+
+stop() {
+    if status ; then
+        docker stop $NAME
+        echo "$NAME stopped"
+    fi
+}
+
+status() {
+    if docker ps --format "{{.Names}}" | grep ^${NAME}$ >/dev/null ; then
+        echo "$NAME running"
+    else
+        echo "$NAME not running"
+        return 1
+    fi
+    return 0
+}
+
+docker_ip() {
+    docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' $NAME    
+}