Add -format to 'docker inspect'

[dustin]

This makes it a lot easier to script with docker instances as one can
ask for details about running instances more easily without having to
have additional JSON processing tools installed.

Note that I did minimal work in separating the current JSON output from the templated output.

#734

Closes #734

[vieux]

Can you give us some example ?

[dustin]

I imagine we'd want a proper docs page with some recipes, but, for example:

% rs=`docker run -P -d dustin/r-studio-server`

Now if you want to know the address it's bound to:

% docker inspect -format='{{.NetworkSettings.IPAddress}}' $rs
172.17.0.3

The structure of the networking section is, IMO, awkward, but workable (port maps to an array of objects). If you wanted a textual list of all portmappings, you could do this:

% docker inspect -format='{{range $p, $conf := .NetworkSettings.Ports}} {{$p}} -> {{(index $conf 0).HostPort}} {{end}}' $rs

which yields

8787/tcp -> 49153

If you wanted the specific external port for that, you could do this:

% docker inspect -format='{{(index (index .NetworkSettings.Ports "8787/tcp") 0).HostPort}}' $rs

yields

49153

That one is particularly awkward, but, again, it's how the structure was defined.

[dustin]

The previous commit update just adds a newline to the error message when your template can't be parsed. No functional change.

[tianon]

Definitely huge +1 from me! I've been wanting someone to implement this one for a while. :)

Getting at these values with nothing but bash as we are right now is cumbersome or requires extra tooling I don't even have installed (and can't justify for just this, especially given that the scripts I write usually run on the machines of other people who definitely won't install jq just for one or two little scripts).

[crosbymichael]

@dustin Can you add the examples to the docs page for inspect?

[dustin]

@crosbymichael I'm happy to provide docs. Do you want them in docs/sources/commandline/cli.rst?

[crosbymichael]

Yes, a few examples under this command in cli.rst would be perfect.

[crosbymichael]

Status's type changed to be a string with a new field StatusCode which is an int.

[dustin]

rebased

[crosbymichael]

LGTM

[vieux]

LGTM