Tune ansible configuration for better performance

This change will update our ansible configuration to ensure we're getting the best
possible performance when running ansible playbooks via mistral.

- sets the ansible option internal_poll_interval so that we lower overall cpu
  consumption.
- sets the ssh option PreferredAuthentications so that we're only offering
  pubkeys when connecting to remote hosts which, in most cases, will save us
  from attempting a PTR lookup.

Change-Id: I421183abd0982f9f57f8719d72fd2cbf2e3d4d04
Signed-off-by: Kevin Carter <kecarter@redhat.com>
(cherry picked from commit 8ab0901ad7)

tripleo_common/actions/ansible.py

@@ -111,6 +111,9 @@ def write_default_ansible_cfg(work_dir,
     config.set('defaults', 'fact_caching_connection',
                '/var/lib/mistral/ansible_fact_cache')
 
+    # Set the pull interval to lower CPU overhead
+    config.set('defaults', 'internal_poll_interval', '0.05')
+
     # Set the interpreter discovery to auto mode.
     config.set('defaults', 'interpreter_python', 'auto')
 
@@ -124,7 +127,8 @@ def write_default_ansible_cfg(work_dir,
                '-o ControlMaster=auto '
                '-o ControlPersist=30m '
                '-o ServerAliveInterval=5 '
-               '-o ServerAliveCountMax=5')
+               '-o ServerAliveCountMax=5 '
+               '-o PreferredAuthentications=publickey')
     config.set('ssh_connection', 'control_path_dir',
                os.path.join(work_dir, 'ansible-ssh'))
     config.set('ssh_connection', 'retries', '8')