Add volume multi attach support

Add volume multi attach support

This patch includes the Cinder changes needed
to support volume multiple attaches.  Nova and
python-cinderclient also need patches associated
to provide support for multiple attachments.

This adds the multiattach flag to volumes.  When a
volume is created, a multiattach flag can be set,
which allows a volume to be attached to more than
one Nova instance or host.  If the multiattach flag is
not set on a volume, it cannot be attached to more
than one Nova instance or host

Each volume attachment is tracked in a
new volume_attachment table.  The attachment id is
the unique identifier for each attachment to an
instance or host.

When a volume is to be detached the attachment
uuid must be passed in to the detach call in
order to determine which attachment should be
removed.  Since a volume can be attached to an
instance and a host, the attachment id is used
as the attachment identifier.

Nova:
https://review.openstack.org/#/c/153033/
https://review.openstack.org/#/c/153038/

python-cinderclient:
https://review.openstack.org/#/c/85856/

Change-Id: I950fa00ed5a30e7758245d5b0557f6df42dc58a3
Implements: blueprint multi-attach-volume
APIImpact