apiv21 API v2.1 authentication authentication availabilityzones availability zones barbican Barbican cache Cache cells cell configdrive config drive ephemeral_storage_encryption ephemeral storage encryption fping fping hyperv HyperV hypervisor hypervisor ironic bare metal ipv6 IPv6 libvirt Libvirt livemigration live migration pci PCI periodic periodic quobyte Quobyte USP volume driver rdp RDP rpc_all all RPC serial_console serial console spice SPICE trustedcomputing trusted computing upgrade_levels upgrade levels vnc VNC volumes volumes wsgi WSGI xen Xen xvpvncproxy XCP VNC proxy