Improve sankey logging.

[anntzer]

Running the sankey_rankine example with an info-level logger on emits a
bunch of logs of the form

The scaled sum of the inputs is 0.039204.
This may cause poor layout.
Consider changing the scale so that the scaled sum is approximately 1.0.

but they are clearly intended as such (some flows are just very small,
and they render fine). Remove that log.

There are also some logs of the form

The sum of the flows is nonzero (-0.002000).
Is the system not at steady state?

Improve them by including the patchlabel, so that one can more easily
figure out the potentially incorrect flow values (one now gets

The sum of the flows is nonzero (-0.002000; patchlabel='\n\nOpen\nheater'); is the system not at steady state?

) (as for the actual values in the example, I guess someone should check
the reference the data comes from).

PR Summary

PR Checklist

• Has Pytest style unit tests
• Code is Flake 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way