qemu: Add @nodemask argument to qemuBuildThreadContextProps()

qemu: Add @nodemask argument to qemuBuildThreadContextProps()

When building a thread-context object (inside of
qemuBuildThreadContextProps()) we look at given memory-backend-*
object and look for .host-nodes attribute. This works, as long as
we need to just copy the attribute value into another
thread-context attribute. But soon we will need to adjust it.
That's the point where having the value in virBitmap comes handy.
Utilize the previous commit, which made
qemuBuildMemoryBackendProps() set the argument and pass it into
qemuBuildThreadContextProps().

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Kristina Hanicova <khanicov@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>