input: Write a python function to create a Kubernetes cluster using environment variables and os.system calls.
  assert create_kubernetes_cluster("AWS", 4) == "Cluster created successfully"
  assert create_kubernetes_cluster("GCP", 2) == "Cluster created successfully"
  assert create_kubernetes_cluster("Azure", 3) == "Cluster created successfully"
output: import os
  
  def create_kubernetes_cluster(provider, num_nodes):
      os.environ['CLOUD_PROVIDER'] = provider
      os.environ['NODE_COUNT'] = str(num_nodes)
      
      command = f"kubectl create cluster --provider={provider} --nodes={num_nodes}"
      exit_code = os.system(command)
      
      if exit_code == 0:
          return "Cluster created successfully"
      else:
          return "Failed to create cluster"