How to run Ansible file in Jenkins using Ansible plugin
Simple one.
You should either add ansible_ssh_extra_args="-o StrictHostKeyChecking=no" to inventory or disableHostKeyChecking: true into Jenkins pipeline script (inside ansiblePlaybook block).

Like this:

ansiblePlaybook(
  colorized: true,
  installation: 'ansible27'
  inventory: '[hostsfile]'
  playbook: '[playbook]'
  disableHostKeyChecking: true
)