Offer id implementation

Signed-off-by: Damien DUPORTAL <damien.duportal@gmail.com>
Merge branch 'cloudstack-provider' of https://github.com/worldline/machine into cloudstack-provider

Signed-off-by: Damien DUPORTAL <damien.duportal@gmail.com>

Conflicts:
	drivers/cloudstack/cloudstack.go