Add framework for basic cr command

Add framework for basic cr command

Establishes a framework for creating subcommands (and adds the
necessary packages to the .vendor environment). Adds a stub of
the first subcommand, firstrun, which installs the cr system.

BUG=605772

[agable, 2016-04-21 22:54:39]

agable@chromium.org changed reviewers:
+ seanmccullough@chromium.org

[agable, 2016-04-21 22:54:40]

No application logic here, yet, but felt it made sense to send just the skeleton
out for review before really digging in.

[seanmccullough, 2016-04-27 18:17:33]

Ok, so thought about this a bit. How about this for a matter of principle: It
would be better for overall code health to only include dependencies that are
actually exercised in the CL. Speculation can lead to excess dependencies and
code bloat. IOW, YAGNI?

So a better first cut might be a humble but concrete cr command, without any of
the framework code.  Just a stand-alone main() that performs some task.

Later go back and re-evaluate how cobra and pflag (and others) might improve
over that stand-alone command (maybe write one or two other bare cr commands
first, even).

Thoughts?

[agable, 2016-04-27 18:30:58]

On 2016/04/27 at 18:17:33, seanmccullough wrote:
> Ok, so thought about this a bit. How about this for a matter of principle: It
would be better for overall code health to only include dependencies that are
actually exercised in the CL. Speculation can lead to excess dependencies and
code bloat. IOW, YAGNI?
> 
> So a better first cut might be a humble but concrete cr command, without any
of the framework code.  Just a stand-alone main() that performs some task.
> 
> Later go back and re-evaluate how cobra and pflag (and others) might improve
over that stand-alone command (maybe write one or two other bare cr commands
first, even).
> 
> Thoughts?

So at the time that I sent this, I was already well on my way down implementing
the actual 'firstrun' command. Just wanted to split it into two pieces for
easier reviewing.

The other piece is that subcommands are already part of the design. I will need
something so that the cr tool has subcommands, and I didn't want to write it on
my own. So, IAmGNI?

That said, cobra/pflag are definitely heavy dependencies, and I can almost
certainly do without them. It's just going to take me a bit longer. I'm working
pulling that dependency out and just parsing os.Args[0] on my own in the
followup CL, so I guess you can pass on reviewing this one for now.

[agable, 2016-04-28 22:50:24]

See https://codereview.chromium.org/1929153002 for a newer version of this CL.