Turn on TLS cert generation by default

Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>
Update VBOX_VERSION to 4.3.18

https://www.virtualbox.org/wiki/Changelog
Merge pull request #563 from aanand/turn-on-tls

Turn on TLS and cert generation by default
Merge pull request #567 from rogeriopradoj/patch-1

Update VBOX_VERSION to 4.3.18