Set proper volume_tmp_dir for cinder-volume in cookbook

[Kui Shi]

when ceph is chosen as volume backend, the "/tmp" dir is used to download/upload volume image file:
e.g.
cinder upload-to-image
cinder create --image-id xxxxxx 10

Cinder volume source code:
==========================
volume/drivers/rbd.py: cfg.StrOpt('volume_tmp_dir',
volume/drivers/rbd.py- default=None,
volume/drivers/rbd.py- help='where to store temporary image files if the volume '
volume/drivers/rbd.py- 'driver does not write them directly to the volume'),

volume/drivers/rbd.py- def copy_volume_to_image(self, context, volume, image_service, image_meta):
volume/drivers/rbd.py- self._ensure_tmp_exists()
volume/drivers/rbd.py-
volume/drivers/rbd.py: tmp_dir = self.configuration.volume_tmp_dir or '/tmp'

==========================

The host on which cinder-volume service run should prepare enough space for /tmp or set proper dir for "volume_tmp_dir".
This setting should be applied in chef cookbook.