Correct Transfer-Encoding framing for cached and proxied responses

[krizhanovsky]

With this commit we remove trailing CRLF for responses returned from the cache and stored with Transfer-Encoding: chunked. Need to test that we do not break message framing and really remove unnecessary CRLF.

• General test verifying chunked encoding, including all the extensions allowed by the RFC
• Test that Tempesta FW blocks responses with invalid encoding
• Test framing and especially trailing part of the message for proxied and cached responses.
• Test trailing headers

With tempesta-tech/tempesta#1418 we might remove Chunked-Encoding from cached responses at all, so the test issue probably must be adjusted. @const-t could you please update the issue after the PR?