We already get the Site via the Channel, so there's no need for a dedicated
RequestFactory: we can just use the right constructor.

This encapsulates config for a given database and is the way to get new
connections.

The `http_proxy` and `HTTPS_PROXY` env vars can be set to a `host[:port]` value which should point to a proxy.

The address of the proxy should be excluded from IP blacklists such as the `url_preview_ip_range_blacklist`.

The proxy will then be used for
 * push
 * url previews
 * phone-home stats
 * recaptcha validation
 * CAS auth validation

It will *not* be used for:
 * Application Services
 * Identity servers
 * Outbound federation
 * In worker configurations, connections from workers to masters

Fixes #4198.

Python will return a tuple whether there are parentheses around the returned values or not.

I'm just sick of my editor complaining about this all over the place :)

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

Hopefully this time we really will fix #4422.

We need to make sure that the cache on
`get_rooms_for_user_with_stream_ordering` is invalidated *before* the
SyncHandler is notified for the new events, and we can now do so reliably via
the `events` stream.

Rather than stubbing out the access_log, make it actually log the requests,
which makes it a lot more obvious what is going on during tests.

two reasons for this. One, it saves a bunch of boilerplate. Two, it squashes
unicode to IDNA-in-a-`str` (even on python 3) in a way that it turns out we
rely on to give consistent behaviour between python 2 and 3.

We want to wait until we have read the response body before we log the request
as complete, otherwise a confusing thing happens where the request appears to
have completed, but we later fail it.

To do this, we factor the salient details of a request out to a separate
object, which can then keep track of the txn_id, so that it can be logged.

Newer syntax

    attr.ib(factory=dict)

is just a syntactic sugar for

    attr.ib(default=attr.Factory(dict))

It was introduced in newest version of attrs package (18.1.0)
and doesn't work with older versions.

We should either require minimum version of attrs to be 18.1.0,
or use older (slightly more verbose) syntax.
Requiring newest version is not a good solution because
Linux distributions may have older version of attrs (17.4.0 in Fedora 28),
and requiring to build (and package)
newer version just to use newer syntactic sugar in only one test
is just too much.
It's much better to fix that test to use older syntax.

Signed-off-by: Oleg Girko <ol@infoserver.lv>