Add Cinder v2 Keystone endpoint support

In Icehouse release, official API supported is v2 but Nova does not
support it at this time.

For now, we keep v1 endpoint for backward compatibility and let the
operator create a v2 endpoint.

Change-Id: I27264dff683c47560351235c8e398afe7c8df2f0
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
move default_volume_type to cinder::api

In a previous commit, this parameter has been introduced in
cinder::backends, but it should be configured on Cinder API server.
This patch deprecated the old parameter.

Change-Id: Ic84c316dc80d8d778ce62df85a6b5bff4a18ead1
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>