Fix issues related to upgrading to Virtualbox 5

[nathanleclaire]

cc @tianon

This seems to fix the issues seen related to using boot2docker-cli with Virtualbox 5, the latest release.

I have tested this patch in the following situations and creating, starting/stopping, day-to-day Docker operations etc. seem to be working normally with the 1.7.1rc3 ISO provided at https://github.com/tianon/boot2docker:

1. On OSX, with Virtualbox 5
2. On Debian (Jessie) Linux, using Virtualbox 4.3.18
3. On Windows, using Virtualbox 4.* (not sure which actually), and then again with Virtualbox 5

Cheers to @hheimbuerger for taking the initiative on a similar patch, I essentially consider this a carrying of his original patch.

Signed-off-by: Nathan LeClaire [email protected]

Closes #373
Fixes #374
Fixes boot2docker/boot2docker#979

[tianon]

🤘 LGTM

Thanks @hheimbuerger for getting us started and thanks @nathanleclaire for carrying us over the finish line. Let's get us a 1.7.1 release! 👍

[nathanleclaire]

👍 👍 👍

[hheimbuerger]

This change means that AddNATPF() (now modifyvm, working on stopped VMs) and DelNATPF() (still controlvm, working on running VMs) are now behaving differently. Was that intentional?

[nathanleclaire]

@hheimbuerger It was not deliberate, although it doesn't seem like it will affect anything as DelNATPF is not invoked in the code anywhere that I can see. Would definitely appreciate a follow-up PR to make it consistent.