services: un-mark group services as deregistered if restart hook runs

This PR may fix a bug where group services will never be deregistered if the
group undergoes a task restart.

client/allocrunner/group_service_hook.go

@@ -119,12 +119,14 @@ func (h *groupServiceHook) Prerun() error {
 	defer func() {
 		// Mark prerun as true to unblock Updates
 		h.prerun = true
+		// Mark deregistered as false to allow de-registration
+		h.deregistered = false
 		h.mu.Unlock()
 	}()
 	return h.preRunLocked()
 }
 
-// caller must hold h.lock
+// caller must hold h.mu
 func (h *groupServiceHook) preRunLocked() error {
 	if len(h.services) == 0 {
 		return nil
@@ -188,6 +190,8 @@ func (h *groupServiceHook) PreTaskRestart() error {
 	defer func() {
 		// Mark prerun as true to unblock Updates
 		h.prerun = true
+		// Mark deregistered as false to allow de-registration
+		h.deregistered = false
 		h.mu.Unlock()
 	}()
 
@@ -201,7 +205,7 @@ func (h *groupServiceHook) PreKill() {
 
 // implements the PreKill hook
 //
-// caller must hold h.lock
+// caller must hold h.mu
 func (h *groupServiceHook) preKillLocked() {
 	// If we have a shutdown delay deregister group services and then wait
 	// before continuing to kill tasks.