Allow plain connection after ssl deny

[G1gg1L3s]

Right now, if some clients receive SSL deny from the server, they can try to start plain connection by sending plain Startup message. The last one would then be served not as a startup, but as a general one, which will hang a connection.

This PR fixes this by reloading client thread after ssl deny to expect startup message again.

There are a couple of TODOs, which I hope you will help me to resolve.

Checklist

• [x] Change is covered by automated tests
• [x] The coding guidelines are followed
• [x] ~Public API has proper documentation in the Acra documentation site or has PR on documentation repository~ with new changes
• [x] ~CHANGELOG.md is updated (in case of notable or breaking changes)~
• [x] CHANGELOG_DEV.md is updated
• [x] ~Benchmark results are attached (if applicable)~
• [x] ~Example projects and code samples are up-to-date (in case of API changes)~