provider/local: fall back to os/user if $USER=""

provider/local: fall back to os/user if $USER=""

If $USER is unset/empty, then fall back to os/user.
If that fails, then return an error.

Fixes lp:1274780

https://code.launchpad.net/~axwalk/juju-core/lp1274780-osuser-fallback/+merge/204173

Requires: https://code.launchpad.net/~axwalk/juju-core/local-provider-testability/+merge/204169

(do not edit description out of merge proposal)

[axw, 2014-01-31 09:11:57]

Please take a look.

[dimitern, 2014-01-31 09:25:07]

LGTM with one comment.

https://codereview.appspot.com/58970043/diff/1/provider/local/environprovider...
File provider/local/environprovider_test.go (right):

https://codereview.appspot.com/58970043/diff/1/provider/local/environprovider...
provider/local/environprovider_test.go:262: userOSErr: errors.New("oh noes"),
You could just define userOSErr as string and construct an error from it in
PatchValue below.

[axw, 2014-01-31 11:36:49]

https://codereview.appspot.com/58970043/diff/1/provider/local/environprovider...
File provider/local/environprovider_test.go (right):

https://codereview.appspot.com/58970043/diff/1/provider/local/environprovider...
provider/local/environprovider_test.go:262: userOSErr: errors.New("oh noes"),
On 2014/01/31 09:25:07, dimitern wrote:
> You could just define userOSErr as string and construct an error from it in
> PatchValue below.

I was going to initially, but it's more long-winded that way. You need to check
if the string != "", and only then create an error. I'll leave it unless you
strongly object.

[thumper, 2014-02-13 21:58:04]

https://codereview.appspot.com/58970043/diff/1/provider/local/environprovider.go
File provider/local/environprovider.go (right):

https://codereview.appspot.com/58970043/diff/1/provider/local/environprovider...
provider/local/environprovider.go:60: username = u.Username
should we lowercase this?

[axw, 2014-02-14 01:03:27]

https://codereview.appspot.com/58970043/diff/1/provider/local/environprovider.go
File provider/local/environprovider.go (right):

https://codereview.appspot.com/58970043/diff/1/provider/local/environprovider...
provider/local/environprovider.go:60: username = u.Username
On 2014/02/13 21:58:04, thumper wrote:
> should we lowercase this?

Nope, *nix usernames are case sensitive.

[thumper, 2014-02-14 01:08:52]

On 2014/02/14 01:03:27, axw wrote:
>
https://codereview.appspot.com/58970043/diff/1/provider/local/environprovider.go
> File provider/local/environprovider.go (right):
> 
>
https://codereview.appspot.com/58970043/diff/1/provider/local/environprovider...
> provider/local/environprovider.go:60: username = u.Username
> On 2014/02/13 21:58:04, thumper wrote:
> > should we lowercase this?
> 
> Nope, *nix usernames are case sensitive.

LGTM