ssh: keep original permissions, when hashing known_hosts

ssh-keygen sets the newly created known_hosts file's permissions to
0600. It's good for user's personal files, but bad idea for the global
ones, like /etc/ssh/ssh_known_hosts. This patch record's the original
file's permissions, and sets them on the hashed one after hashing.

salt/modules/ssh.py

@@ -1175,8 +1175,10 @@ def hash_known_hosts(user=None, config=None):
     if not os.path.isfile(full):
         return {'status': 'error',
                 'error': 'Known hosts file {0} does not exist'.format(full)}
+    origmode = os.stat(full).st_mode
     cmd = ['ssh-keygen', '-H', '-f', full]
     cmd_result = __salt__['cmd.run'](cmd, python_shell=False)
+    os.stat(full, origmode)
     # ssh-keygen creates a new file, thus a chown is required.
     if os.geteuid() == 0 and user:
         uinfo = __salt__['user.info'](user)