Order imports in alphabetical order (8/9)

This patch is one in a series to re-enable H306 style check rule
(imports are in alphabetical order).
It touches second half of tests (starting from test_n*).

Implements: blueprint reduce-flake8-ignored-rules (partial)
Change-Id: I5561d90a67eb5dc882200d432fda6b162011ac41
Merge "Order imports in alphabetical order (8/9)"