Updates to allow for using an enterprise specific token as the agents token

This is needed to allow for managed Consul instances to register themselves in the catalog with one of the managed service provider tokens.

agent/token/store.go

@@ -113,6 +113,10 @@ func (t *Store) AgentToken() string {
 	t.l.RLock()
 	defer t.l.RUnlock()
 
+	if tok := t.enterpriseAgentToken(); tok != "" {
+		return tok
+	}
+
 	if t.agentToken != "" {
 		return t.agentToken
 	}

agent/token/store_oss.go

@@ -5,3 +5,8 @@ package token
 // Stub for enterpriseTokens
 type enterpriseTokens struct {
 }
+
+// enterpriseAgentToken OSS stub
+func (s *Store) enterpriseAgentToken() string {
+	return ""
+}