cartridge: fix discovery to avoid missing aliases

Implementation of cartridge bootstrap in `tt` needs to know aliases of
all instances to work properly. Aliases of instances are managed with
`membership` module which spreads out certain instance alias across the
rest of instances using `gossip` protocol. At the very start of
an instance only that instance "knows" its alias, others get this
knowledge with some delay. That means in turn that the topology obtained
from the different instances might differ in terms of aliases.

Prior to this patch topology from a single instance was used and if at
that moment this instance haven't collected information about all the
aliases, bootstrap failed. Now if any alias is missing we are trying to
get it from the topologies obtained from the other instances until all
aliases are resolved.

The patch fixes flaky test so there is not need to introduce new tests.

Closes #TNTP-3709

Author: elhimov

cli/replicaset/cartridge.go

@@ -245,14 +245,16 @@ func (c *CartridgeApplication) discovery() (Replicasets, error) {
 			}
 			if topology.IsBootstrapped {
 				if newTopology.IsBootstrapped {
+					updateInstancesAliases(newTopology.Replicasets, topology.Replicasets)
 					topology = newTopology
 				}
 			} else {
 				topology = newTopology
 			}
 
 			// Stop if we already found a valid topology.
-			return topology.IsBootstrapped && !topology.IsCritical, nil
+			return topology.IsBootstrapped && !topology.IsCritical &&
+				!hasMissingInstancesAliases(topology.Replicasets), nil
 		},
 	))
 	if err != nil {
@@ -271,6 +273,37 @@ func (c *CartridgeApplication) discovery() (Replicasets, error) {
 	return recalculateMasters(replicasets), err
 }
 
+// hasMissingInstancesAliases checks if any instance has empty alias.
+func hasMissingInstancesAliases(replicasets []Replicaset) bool {
+	for _, rs := range replicasets {
+		for _, inst := range rs.Instances {
+			if len(inst.Alias) == 0 {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+// updateInstancesAliases tries to update missing instances aliases with another instances data.
+func updateInstancesAliases(replicasets, other []Replicaset) {
+	instAliases := make(map[string]string, 0)
+	for _, rs := range other {
+		for _, inst := range rs.Instances {
+			instAliases[inst.UUID] = inst.Alias
+		}
+	}
+	for i, rs := range replicasets {
+		for ii, inst := range rs.Instances {
+			if len(inst.Alias) == 0 {
+				if alias, ok := instAliases[inst.UUID]; ok && len(alias) > 0 {
+					replicasets[i].Instances[ii].Alias = alias
+				}
+			}
+		}
+	}
+}
+
 // Promote promotes an instance in the cartridge application.
 func (c *CartridgeApplication) Promote(ctx PromoteCtx) error {
 	replicasets, err := c.Discovery(UseCache)