Only run memcached tests if server is available.

tests/lib/memcache/memcached.php

@@ -10,6 +10,13 @@
 namespace Test\Memcache;
 
 class Memcached extends Cache {
+	static public function setUpBeforeClass() {
+		$instance = new \OC\Memcache\Memcached(uniqid());
+		if ($instance->set(uniqid(), uniqid()) === false) {
+			self::markTestSkipped('memcached server seems to be down.');
+		}
+	}
+
 	public function setUp() {
 		if (!\OC\Memcache\Memcached::isAvailable()) {
 			$this->markTestSkipped('The memcached extension is not available.');