Part of #9744

Removes all redundant `# -*- coding: utf-8 -*-` lines from files, as python 3 automatically reads source code as utf-8 now.

`Signed-off-by: Jonathan de Jong <jonathan@automatia.nl&gt;`>

Fix the test to pass the right number of args to the Store constructors

setup_test_homeserver function in utils.

Neaten more of the storage layer tests with assertObjectHasAttributes; more standardisation on test layout

Need to prepare() the SQLiteMemoryDbPool before passing it to HomeServer constructor, as DataStore's constructor will want it ready