add export and import

[waitingkuo]

It's the implementation for #23

To export a machine, you can type

machine export MACHINE_NAME

to get a tar file.

Then you can use

machine import TAR_FILE

to import it in another computer.

[bfirsh]

These should be in alphabetical order.

[bfirsh]

Thanks so much! In addition to IRL comments, I've added some comments to the commits here.

[bfirsh]

To document what I said IRL: I think machine export should output the tar file to stdout, and machine import should read the tar file from stdin, like docker export/import.

[waitingkuo]

Since commands.go changes, I'm going to refactoring. Here's my think:

1. add a tar.go to deal with tar create and tar extract
2. move the export & import logic into store
3. modify export & import commands to suit the new format.

There're three options for adding a tar.go
a. use os/exec call the command line utility tar cv and tar xv
b. use go standard lib tar to build our own. it's my original design, but the format isn't same as the command-line one. We might need to align the block size to make it compatible of the command line tar
c. use the tar util in docker/docker.

which one is better?

[ehazlett]

@waitingkuo would you mind syncing up with @sthulb on this? I can see where this would be useful. #260 is very close to this and I think we should all come together to decide how this should work. There are a couple of things like the format, what should be exported, what to do with machines that cannot be exported (local vs. remote), etc. Thanks!

[ehazlett]

Closing as this has stagnated. Please re-open to start the discussion again. You can also put comments in #260 as well. Thanks!

[waitingkuo]

Hi @ehazleet Sorry for the late reply. Just came back from a trip. I'll take a look #260 and join the discussion soon.