Enable host_key checking at the strategy level

Implements a new method in the ssh connection plugin (fetch_and_store_key)
which is used to prefetch the key using ssh-keyscan.

lib/ansible/utils/connection.py

@@ -0,0 +1,50 @@
+# (c) 2015, Ansible, Inc. <support@ansible.com>
+#
+# This file is part of Ansible
+#
+# Ansible is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Ansible is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
+
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+import subprocess
+import sys
+
+
+__all__ = ['get_smart_connection_type']
+
+def get_smart_connection_type(play_context):
+    '''
+    Uses the ssh command with the ControlPersist option while checking
+    for an error to determine if we should use ssh or paramiko. Also
+    may take other factors into account.
+    '''
+
+    conn_type = 'ssh'
+    if sys.platform.startswith('darwin') and play_context.password:
+        # due to a current bug in sshpass on OSX, which can trigger
+        # a kernel panic even for non-privileged users, we revert to
+        # paramiko on that OS when a SSH password is specified
+        conn_type = "paramiko"
+    else:
+        # see if SSH can support ControlPersist if not use paramiko
+        try:
+            cmd = subprocess.Popen(['ssh','-o','ControlPersist'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+            (out, err) = cmd.communicate()
+            if "Bad configuration option" in err or "Usage:" in err:
+                conn_type = "paramiko"
+        except OSError:
+            conn_type = "paramiko"
+
+    return conn_type