* Pull config_dir_path and data_dir_path calculation out of read_config_files

* Pass config_dir_path and data_dir_path into read_config

Migrate all tests to use the dict-based config format instead of hanging items off HomeserverConfig (#5171)

This endpoint isn't much use for its intended purpose if you first need to get
yourself an admin's auth token.

I've restricted it to the `/_synapse/admin` path to make it a bit easier to
lock down for those concerned about exposing this information. I don't imagine
anyone is using it in anger currently.

I got fed up with always adding '@unittest.DEBUG' every time I needed to debug a test.

Allow for the creation of a support user.

A support user can access the server, join rooms, interact with other users, but does not appear in the user directory nor does it contribute to monthly active user limits.

* Add better diagnostics to flakey keyring test

* fix interpolation fail

* Check logcontexts before and after each test

* update changelog

* update changelog

* Some words about garbage collections and logcontexts

* Do a GC after each test to fix logcontext leaks

This feels like an awful hack, but...

* changelog

Signed-off-by: Schnuffle <schnuffle@github.com>

1. Give the handler used for logging in unit tests a formatter, so that the
output is slightly more meaningful

2. Log some synapse.storage stuff, because it's useful.

Don't make @unittest.DEBUG print the huge amount of verbosity generated by the synapse.storage loggers

Define a CLOS-like 'around' modifier as a decorator, to neaten up the 'orig_*' noise of wrapping the setUp()/tearDown() methods