Simplify summary text.

[CyrusNajmabadi]

Fixes: #2051

Tweaks how we output summary text. Main points:

1. Always one less line than before due to merging 'total changes. unchanged' info into one line.
2. don't show total-changes if it is redundant with the changes we are showing. i.e. don't show 10 changes if we only are showing + 10 to create
3. show the total summary after the individual pieces. i think this just makes more sense since it's the sum of all the little operations we're making.

Multiple changes:

One type of change:

No changes:

All changes:

[chrsmith]

It looks like this is fine, but could you double check the new formatting won't break the unfortunate hack we currently have in the service for grepping the output? Specifically, that we still have have whitespace in front of every line that lists a kind of resource change, and then a blank line at the very end. (Once we send the actual engine events to the service we won't need to rely on that approach...)

https://github.com/pulumi/pulumi-service/blob/master/cmd/service/services/cloud/util.go#L97
https://github.com/pulumi/pulumi-service/blob/master/cmd/service/services/cloud/util_test.go#L36

[CyrusNajmabadi]

Specifically, that we still have have whitespace in front of every line that lists a kind of resource change, and then a blank line at the very end.

Yup. That part should be fine. There should still always be at least one line. And it's still lines that start with 4 spaces, and a final blank line.

Note: those test files will likely be affected here if they are actually validating real output. If they're just validating that you can strip color codes though, it should be ok.