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.

libvirttest/libvirt.go

@@ -94,6 +94,19 @@ var testDisconnectReply = []byte{
 	0x00, 0x00, 0x00, 0x00, // status
 }
 
+var testMigrateReply = []byte{
+	0x00, 0x00, 0x00, 0x20, // length
+	0x20, 0x00, 0x80, 0x86, // program
+	0x00, 0x00, 0x00, 0x01, // version
+	0x00, 0x00, 0x01, 0x31, // procedure
+	0x00, 0x00, 0x00, 0x01, // type
+	0x00, 0x00, 0x00, 0x00, // serial
+	0x00, 0x00, 0x00, 0x00, // status
+
+	// cookie out: 0
+	0x00, 0x00, 0x00, 0x00,
+}
+
 var testRunReply = []byte{
 	0x00, 0x00, 0x00, 0x74, // length
 	0x20, 0x00, 0x80, 0x87, // program
@@ -262,6 +275,8 @@ func (m *MockLibvirt) handleRemote(procedure uint32, conn net.Conn) {
 		conn.Write(m.reply(testDomainsReply))
 	case constants.ProcDomainMigrateSetMaxSpeed:
 		conn.Write(m.reply(testSetSpeedReply))
+	case constants.ProcMigratePerformParams:
+		conn.Write(m.reply(testMigrateReply))
 	}
 }