[Dnode / Vnode] More error handling.

This patch adds more error handling code:
1. In dnodeAllocateWqueue(), if the allocation of pWorker fails, any
allocated memory should be unwound and returns a NULL queue. This is
a better function contract where either all allocation succeeds or none
succeeds.
2. In vnodeOpen(), handle allocation failure for pVnode.

src/dnode/src/dnodeModule.c

@@ -73,7 +73,7 @@ static void dnodeAllocModules() {
 }
 
 void dnodeCleanUpModules() {
-  for (int32_t module = 1; module < TSDB_MOD_MAX; ++module) {
+  for (EModuleType module = 1; module < TSDB_MOD_MAX; ++module) {
     if (tsModule[module].enable && tsModule[module].stopFp) {
       (*tsModule[module].stopFp)();
     }

src/dnode/src/dnodeWrite.c

@@ -120,10 +120,18 @@ void *dnodeAllocateWqueue(void *pVnode) {
 
   if (pWorker->qset == NULL) {
     pWorker->qset = taosOpenQset();
-    if (pWorker->qset == NULL) return NULL;
+    if (pWorker->qset == NULL) {
+      taosCloseQueue(queue);
+      return NULL;
+    }
 
     taosAddIntoQset(pWorker->qset, queue, pVnode);
     pWorker->qall = taosAllocateQall();
+    if (pWorker->qall == NULL) {
+      taosCloseQset(pWorker->qset);
+      taosCloseQueue(queue);
+      return NULL;
+    }
     wWorkerPool.nextId = (wWorkerPool.nextId + 1) % wWorkerPool.max;
 
     pthread_attr_t thAttr;
@@ -132,7 +140,10 @@ void *dnodeAllocateWqueue(void *pVnode) {
 
     if (pthread_create(&pWorker->thread, &thAttr, dnodeProcessWriteQueue, pWorker) != 0) {
       dError("failed to create thread to process read queue, reason:%s", strerror(errno));
+      taosFreeQall(pWorker->qall);
       taosCloseQset(pWorker->qset);
+      taosCloseQueue(queue);
+      queue = NULL;
     } else {
       dTrace("write worker:%d is launched", pWorker->workerId);
     }

src/vnode/src/vnodeMain.c

@@ -176,6 +176,9 @@ int32_t vnodeOpen(int32_t vnode, char *rootDir) {
   pthread_once(&vnodeModuleInit, vnodeInit);
 
   SVnodeObj *pVnode = calloc(sizeof(SVnodeObj), 1);
+  if (pVnode == NULL) {
+    return TSDB_CODE_NO_RESOURCE;
+  }
   pVnode->vgId     = vnode;
   pVnode->status   = TAOS_VN_STATUS_INIT;
   pVnode->refCount = 1;