Add 'update_hash' and 'list' to tool/ports

Issue #1082
Enable hash checks for ports mechanism
rtc: document current interface

Issue #1148
vfs: catch lookup-failed exception on node discovery
nova: re-throw uncatched exception of dying thread

If the re-throw works, we will can see which exception type was thrown.
vmm utils: cpu-session parameter for VMM thread

Issue #1157
vbox: update to 4.2.24
vbox: enable guest additions

Fixes #1157