tools: initialize main loop before block layer

Tools were broken because they initialized the block layer while
qemu_aio_context was still NULL.
Reported-by: Nmalc <av1474@comtv.ru>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Nmalc <av1474@comtv.ru>

qemu-img.c

@@ -2001,14 +2001,13 @@ int main(int argc, char **argv)
 
     error_set_progname(argv[0]);
 
+    qemu_init_main_loop();
     bdrv_init();
     if (argc < 2)
         help();
     cmdname = argv[1];
     argc--; argv++;
 
-    qemu_init_main_loop();
-
     /* find the command */
     for(cmd = img_cmds; cmd->name != NULL; cmd++) {
         if (!strcmp(cmdname, cmd->name)) {

qemu-io.c

@@ -1892,9 +1892,8 @@ int main(int argc, char **argv)
         exit(1);
     }
 
-    bdrv_init();
-
     qemu_init_main_loop();
+    bdrv_init();
 
     /* initialize commands */
     quit_init();