qemu: Create base hugepages path on memory hotplug

qemu: Create base hugepages path on memory hotplug

Users can play all sorts of games with mount points. For
instance, they can unmount and mount back a hugetlbfs and only
after that attempt to hotplug memory.

This has an unfortunate consequence though. During memory
hotplug, when qemuProcessBuildDestroyMemoryPaths() is called the
path is created with very restrictive mode (0700) because under
the hood g_mkdir_with_parents(path, 0700) is called.

Therefore, create the driver generic portion of the path
separately.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2134009
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Erik Skultety <eskultet@redhat.com>