cloud: use machine_id for all agent communication

The original proto used provider-scoped provider_ids, these are being
replaced by  a single machine_id, assigned by the BMaaS service.
Its API works in terms of machine_id, not provider_id (see
AgentHeartbeatRequest), so this needs to be changed.

Change-Id: If13942d02a8ac0e2901c549a92a67b6b10a1e196
Reviewed-on: https://review.monogon.dev/c/monogon/+/1263
Tested-by: Leopold Schabel <leo@monogon.tech>
Reviewed-by: Leopold Schabel <leo@monogon.tech>
diff --git a/cloud/takeover/e2e/main_test.go b/cloud/takeover/e2e/main_test.go
index 9788bd5..2b15174 100644
--- a/cloud/takeover/e2e/main_test.go
+++ b/cloud/takeover/e2e/main_test.go
@@ -181,8 +181,7 @@
 	defer sess.Close()
 
 	init := api.TakeoverInit{
-		Provider:      "test",
-		ProviderId:    "test1",
+		MachineId:     "test",
 		BmaasEndpoint: "localhost:1234",
 	}
 	initRaw, err := proto.Marshal(&init)