Add port verification to start server in kanidm_client tests

Ports could be already allocated and tests start failing depending on the
execution environment.

kanidm_client/tests/common.rs

@@ -1,4 +1,5 @@
-use std::sync::atomic::{AtomicUsize, Ordering};
+use std::net::TcpStream;
+use std::sync::atomic::{AtomicU16, Ordering};
 use std::thread;
 
 use kanidm::audit::LogLevel;
@@ -10,7 +11,14 @@ use async_std::task;
 use tokio::sync::mpsc;
 
 pub const ADMIN_TEST_PASSWORD: &str = "integration test admin password";
-static PORT_ALLOC: AtomicUsize = AtomicUsize::new(8080);
+static PORT_ALLOC: AtomicU16 = AtomicU16::new(8080);
+
+fn is_free_port(port: u16) -> bool {
+    match TcpStream::connect(("0.0.0.0", port)) {
+        Ok(_) => false,
+        Err(_) => true,
+    }
+}
 
 // Test external behaviours of the service.
 
@@ -25,7 +33,12 @@ pub fn run_test(test_fn: fn(KanidmClient) -> ()) {
     let (mut ready_tx, mut ready_rx) = mpsc::channel(1);
     let (mut finish_tx, mut finish_rx) = mpsc::channel(1);
 
-    let port = PORT_ALLOC.fetch_add(1, Ordering::SeqCst);
+    let port = loop {
+        let possible_port = PORT_ALLOC.fetch_add(1, Ordering::SeqCst);
+        if is_free_port(possible_port) {
+            break possible_port;
+        }
+    };
 
     let int_config = Box::new(IntegrationTestConfig {
         admin_password: ADMIN_TEST_PASSWORD.to_string(),