Fix k8s node join time not enough issue (sonic-net#20141)

What is the motivation for this PR?
It's an improvement for testbed vms75-t0-7050cx3-1. For this SKU, the kubelet needs more time(around 70s) to join the minikube cluster.

How did you do it?
Increased the wait time for joining node to cluster.

How did you verify/test it?
Run this test in testbed vms75-t0-7050cx3-1 to see if it passes.

Author: lixiaoyuner

tests/kubesonic/test_k8s_join_disjoin.py

@@ -361,11 +361,13 @@ def trigger_join_and_check(duthost, vmhost):
     logger.info("Start to join duthost to k8s cluster and check the status")
     duthost.shell(f"sudo config kube server ip {vmhost.mgmt_ip}")
     duthost.shell("sudo config kube server disable off")
-    time.sleep(60)
-    nodes = vmhost.shell(f"{NO_PROXY} minikube kubectl -- get nodes {duthost.hostname}", module_ignore_errors=True)
-    pytest_assert(duthost.hostname in nodes["stdout"], "Failed to join duthost to k8s cluster")
-    pytest_assert("NotReady" not in nodes["stdout"], "The status of duthost in k8s cluster is not ready")
-    logger.info(f"Successfully joined duthost {duthost.hostname} to k8s cluster")
+    for _ in range(12):
+        time.sleep(10)
+        nodes = vmhost.shell(f"{NO_PROXY} minikube kubectl -- get nodes {duthost.hostname}", module_ignore_errors=True)
+        if duthost.hostname in nodes["stdout"] and "NotReady" not in nodes["stdout"]:
+            logger.info("Duthost is successfully joined to k8s cluster")
+            return
+    pytest_assert(False, "Failed to join duthost to k8s cluster")
 
 
 def trigger_disjoin_and_check(duthost, vmhost):