Refactor tests.unit.utils:FakeDB.reset

glance.tests.unit.utils:FakeDB uses glance.db.simple.api which has
already implemented reset() functionality, the redundant code in
FakeDB should be removed.

Change-Id: I140e932e9cc531900cee503e20d3549549b13d27
Closes-Bug: #1264204
Fix and enable gating on H306

Fix fallout of Hacking check: Imports should be in alphabetical order

Change-Id: I179711c8448208592490ffa47d51419779940014
Merge "Refactor tests.unit.utils:FakeDB.reset"
Merge "Fix and enable gating on H306"