Consider renaming `spine-stackdriver-trace`

[yuri-sergiichuk]

The whole "Stackdriver" branding was dropped by Google in favor of "Cloud" branding. The "Stackdriver" itself is renamed to "Cloud Operations suite" while Trace is renamed to Cloud Trace.

I'd consider renaming spine-stackdriver-trace to either spine-trace or spine-cloud-trace.

[armiol]

@yuri-sergiichuk I'd rename to spine-cloud-trace. And I would do that in 1.7.

[alexander-yevsyukov]

Let's do it in v2.0. The renaming is a breaking change. It's better not overload 1.7 with too many incompatible changes.
And let's release v2.0 sooner.