Add support for domain migrations

This adds basic support for domain migrations from one hypervisor to
another. Migration options, e.g., live, tunneled, compressed, etc..,
are specified by the constants described `constants.Migrate*`.

Two unknowns remain, Libvirt specifies `RemoteParameters` and `CookieIn`.
In testing both values are always set to 0 by `virsh` and the source
does not provide clear definitions of their purpose. For now, using
the same zero'd values used by `virsh` will be Good Enough.

internal/constants/constants.go

@@ -29,10 +29,11 @@ const (
 	ProcConnectOpen              = 1
 	ProcConnectClose             = 2
 	ProcDomainLookupByName       = 23
-	ProcDomainMigrateSetMaxSpeed = 207
 	ProcAuthList                 = 66
 	ProcConnectGetLibVersion     = 157
+	ProcDomainMigrateSetMaxSpeed = 207
 	ProcConnectListAllDomains    = 273
+	ProcMigratePerformParams     = 305
 )
 
 // qemu procedure identifiers