core: add host_provider_id to vdsStatic

This allows to sign the provider id, which in hosts mostly foreman
server id that added as external provider. With saving the ID we'll be
able to gather more info about the host later on.

Change-Id: Icced7dda43fee83aa904a068cff48b1fd3da4b76
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1113003
Signed-off-by: Yaniv Bronhaim <ybronhei@redhat.com>