Mark user creation tests as slow

Mark the "should not create the user if not instructed to" and "should
create the user if instructed to" tests as slow as these take more than
2 seconds to execute on travis.

test/integration/clusterio.js

@@ -197,6 +197,7 @@ describe("Integration of Clusterio", function() {
 				}
 			});
 			it("should not create the user if not instructed to", async function() {
+				slowTest(this);
 				for (let list of lists) {
 					try {
 						await execCtl(`user set-${list} no_create_test`);
@@ -206,6 +207,7 @@ describe("Integration of Clusterio", function() {
 				assert.equal(user, undefined, "user was unexpectedly created");
 			});
 			it("should create the user if instructed to", async function() {
+				slowTest(this);
 				for (let list of lists) {
 					await execCtl(`user set-${list} --create test_create_${list}`);
 					let user = (await getUsers()).get(`test_create_${list}`);