Order imports in alphabetical order (4/9)

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

Implements: blueprint reduce-flake8-ignored-rules (partial)
Change-Id: I66842c6a5d112f948e625e18ef6d01afcad61e57
Merge "Order imports in alphabetical order (4/9)"