Fixes https://github.com/turt2live/matrix-media-repo/issues/318

In various places in the code base, the address and port are joined using a `:`.
This causes issues with IPv6-addresses (see #247).
Address this by using net.JoinHostPort everywhere.

Signed-off-by: Silke Hofstra <silke@slxh.eu>

Fixes https://github.com/turt2live/matrix-media-repo/issues/188

And then stripped from the serverName when checking the cert

This should help memory some more. See https://github.com/turt2live/matrix-media-repo/issues/237

Theory is that by dumping the streams we'll relieve any bytes held on by the S3 libraries. 

We'd return a 500 when the token isn't found on the homeserver, but we should be returned a proper auth error. This just fixes the logic around the area to make that actually work.

Fixes https://github.com/turt2live/matrix-media-repo/issues/63

Fixes https://github.com/turt2live/matrix-media-repo/issues/209

Part of https://github.com/turt2live/matrix-media-repo/issues/209

Part of https://github.com/turt2live/matrix-media-repo/issues/209

Fixes https://github.com/turt2live/matrix-media-repo/issues/162