review-page: Apply all deferred property changes

That's a funny one: Boxes has a clever mechanism to avoid changing
properties constantly (it can be UI blocking to change some of the
properties, for example, the storage disk needs to be resized when
the user changes the size on the GtkScale). The mechanism basically
adds a timeout for properties to be applied later.

Unfortunately, we can't shrink disks, therefore when it comes to
storage size, we don't use the timeout mechanism mentioned above.
This way, the properties need to be applied manually when the user
is ready-to-create the VM.

When adding the new VM Assistant, I didn't account for that, hence
this uggly regression.

Fixes #514
Fixes #515
2 jobs for apply-deferred-property-changes in 51 minutes and 18 seconds
Status Job ID Name Coverage
  Test
passed #671897
flatpak
flatpak

00:44:13

 
  Fedora
passed #671898
fedora:rawhide

00:07:05