demo: support launchpad entries with mem >= 2048M

Fixes #1325
vmm: fix overmap attempts by seoul and vbox

If the debug branch of the nova kernel is used, following messages are printed
by the kernel during vCPU setup phase:

[0] overmap attempt OBJ - tree - ...

Fixes #1324
vbox: use power of two priority levels

Avoids warnings of init in form of

"priority band too small, losing least-significant priority bits"

when virtualbox starts threads.

Fixes #1323
vbox: support absolute mouse input events

Got broken during upgrade from 4.2 to 4.3.

Fixes #1321