tree-wide: Update to new libglnx fd APIs

This ends up a lot better IMO.  This commit is *mostly* just
`s/glnx_close_fd/glnx_autofd`, but there's also a number of hunks like:

```
-  if (self->sysroot_fd != -1)
-    {
-      (void) close (self->sysroot_fd);
-      self->sysroot_fd = -1;
-    }
+  glnx_close_fd (&self->sysroot_fd);
```

Update submodule: libglnx

Closes: #1259
Approved by: jlebon

src/libostree/ostree-bootloader-uboot.c

@@ -73,7 +73,7 @@ append_system_uenv (OstreeBootloaderUboot   *self,
                     GCancellable            *cancellable,
                     GError                 **error)
 {
-  glnx_fd_close int uenv_fd = -1;
+  glnx_autofd int uenv_fd = -1;
   __attribute__((cleanup(_ostree_kernel_args_cleanup))) OstreeKernelArgs *kargs = NULL;
   const char *uenv_path = NULL;
   const char *ostree_arg = NULL;