virThreadPoolFree: Join worker threads

Even though currently we are freeing the pool of worker threads at the
daemon very end, nothing holds us back in joining the worker threads.
Moreover, we avoid leaks like this:

==26697== 1,680 bytes in 5 blocks are possibly lost in loss record 913 of 942
==26697==    at 0x4C2BDE4: calloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==26697==    by 0x4011131: allocate_dtv (in /lib64/ld-2.16.so)
==26697==    by 0x401176D: _dl_allocate_tls (in /lib64/ld-2.16.so)
==26697==    by 0x8499602: pthread_create@@GLIBC_2.2.5 (in /lib64/libpthread-2.16.so)
==26697==    by 0x52F53E9: virThreadCreate (virthreadpthread.c:188)
==26697==    by 0x52F5D4F: virThreadPoolNew (virthreadpool.c:221)
==26697==    by 0x53F30DB: virNetServerNew (virnetserver.c:377)
==26697==    by 0x11C6ED: main (libvirtd.c:1366)
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

src/util/virthreadpool.c

@@ -241,6 +241,9 @@ void virThreadPoolFree(virThreadPoolPtr pool)
 {
     virThreadPoolJobPtr job;
     bool priority = false;
+    size_t i;
+    size_t nWorkers = pool->nWorkers;
+    size_t nPrioWorkers = pool->nPrioWorkers;
 
     if (!pool)
         return;
@@ -262,6 +265,12 @@ void virThreadPoolFree(virThreadPoolPtr pool)
         VIR_FREE(job);
     }
 
+    for (i = 0; i < nWorkers; i++)
+        virThreadJoin(&pool->workers[i]);
+
+    for (i = 0; i < nPrioWorkers; i++)
+        virThreadJoin(&pool->prioWorkers[i]);
+
     VIR_FREE(pool->workers);
     virMutexUnlock(&pool->mutex);
     virMutexDestroy(&pool->mutex);