Change default of where stack is created

[justinvp]

If currently logged in, stack init creates a managed stack. Otherwise, it creates a local stack. This avoids the need to specify --local when not using the service.

As today, --local can be passed, which will create a local stack regardless of being logged in or not.

A new flag, --remote, has been added, which can be passed to indicate a managed stack, used to force an error if not logged into the service.

Fixes #816

[ellismg]

LGTM. Sorry for the delay, thought I reviewed this yesterday!

[justinvp]

@ellismg, No problem.

I was about to merge this and looked over the changes again and I realized I made a mistake when factoring out the "is logged in" check to its own function. If we want to keep it factored this way, cloudURL needs to be passed as a pointer so its value can be changed to the default URL when empty, since cloudURL is then used subsequently when creating the cloud backend. Not sure how I missed this while I was manually testing the change earlier. The test suite didn't catch it as the cloud tests only run when PULUMI_API is set, which is then used to set --cloud-url explicitly (so cloudURL would never be empty). It'd be nice to add a regression test for this, but I don't think we want the tests using the default URL. In any case, I manually confirmed when logged-in pulumi stack init foo fails before the new commit and works as expected after the new commit.

Mind taking a quick look at the new commit?

[ellismg]

It it possible to restructure the code such that we use cloud.ValueOrDefaultURL(string), instead (like maybe at the start of the function that handles the cobra commands)? I think that would let us remove the by reference stuff. If the code ends up looking worse adopting that, then we can go with this instead, just feels a little strange.

[justinvp]

Sure, I'll change it to that.

[ellismg]

LGTM