Add support for keystone_ec2_url

This patch adds support for configuring the keystone_ec2_url
needed to provide EC2 API support in nova-api-ec2

Change-Id: If37c5e9475299b28f0ccd2a45ab61dd6adabf73a
Configure novav3 service only if v3 endpoing is enabled

Change-Id: Ib229ec381c8baf8c9f90652eddc30ce9fd5a4ace
Merge "Configure novav3 service only if v3 endpoing is enabled"