nixos/tests/openssh: add timeouts to all ssh invocations

It might still lock up, but at least it won't lock up for 10 hours.

nixos/tests/openssh.nix

@@ -80,17 +80,21 @@ in {
 
         client.wait_for_unit("network.target")
         client.succeed(
-            "ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no server 'echo hello world' >&2"
+            "ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no server 'echo hello world' >&2",
+            timeout=30
         )
         client.succeed(
-            "ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no server 'ulimit -l' | grep 1024"
+            "ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no server 'ulimit -l' | grep 1024",
+            timeout=30
         )
 
         client.succeed(
-            "ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no server_lazy 'echo hello world' >&2"
+            "ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no server_lazy 'echo hello world' >&2",
+            timeout=30
         )
         client.succeed(
-            "ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no server_lazy 'ulimit -l' | grep 1024"
+            "ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no server_lazy 'ulimit -l' | grep 1024",
+            timeout=30
         )
 
     with subtest("configured-authkey"):
@@ -99,10 +103,12 @@ in {
         )
         client.succeed("chmod 600 privkey.snakeoil")
         client.succeed(
-            "ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no -i privkey.snakeoil server true"
+            "ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no -i privkey.snakeoil server true",
+            timeout=30
         )
         client.succeed(
-            "ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no -i privkey.snakeoil server_lazy true"
+            "ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no -i privkey.snakeoil server_lazy true",
+            timeout=30
         )
 
     with subtest("localhost-only"):