Order imports in alphabetical order (2/9)

This patch is one in a series to re-enable H306 style check rule
(imports are in alphabetical order). It touches API files.

Implements: blueprint reduce-flake8-ignored-rules (partial)
Change-Id: I81c7c79516ce1a17055c3b9c12a94312ed3d1940
Merge "Order imports in alphabetical order (2/9)"