client: Give a copy of clientconfig to allocrunner

Currently, there is a race condition between creating a taskrunner, and
updating node attributes via fingerprinting.

This is because the taskenv builder will try to iterate over the
clientconfig.Node.Attributes map, which can be concurrently updated by
the fingerprinting process, thus causing a panic.

This fixes that by providing a copy of the clientconfg to the
allocrunner inside the Read lock during config creation.

client/client.go

@@ -867,7 +867,7 @@ func (c *Client) restoreState() error {
 		arConf := &allocrunner.Config{
 			Alloc:                 alloc,
 			Logger:                c.logger,
-			ClientConfig:          c.config,
+			ClientConfig:          c.configCopy,
 			StateDB:               c.stateDB,
 			StateUpdater:          c,
 			DeviceStatsReporter:   c,
@@ -2059,7 +2059,7 @@ func (c *Client) addAlloc(alloc *structs.Allocation, migrateToken string) error
 	arConf := &allocrunner.Config{
 		Alloc:                 alloc,
 		Logger:                c.logger,
-		ClientConfig:          c.config,
+		ClientConfig:          c.configCopy,
 		StateDB:               c.stateDB,
 		Consul:                c.consulService,
 		Vault:                 c.vaultClient,