Sheepdog and possibly others use nested objects for network server and
thus could be specified in a way that libvirt would not parse.
Validates that https://bugzilla.redhat.com/show_bug.cgi?id=1464821
is fixed properly.
As it turns out sometimes users pass in an arbitrarily nested structure
e.g. for the qemu backing chains JSON pseudo protocol. This new
implementation deflattens now a single object fully even with nested
keys.
Additionally it's not necessary now to stick with the "file." prefix for
the properties.
