you will need to pass the content of the "/home/ec2-user/.ssh/id_rsa".

Example:

id_rsa = ''

with open("/home/ec2-user/.ssh/id_rsa", 'r') as f:
  id_rsa = f.read()

cmd = cm.host_install(host_username, host_list, private_key=id_rsa, cm_repo_url=cm_repo_url)