benchmark: extracted TLS server script

Refactored out the TLS server into a script that can be run on it's own.

Modified tls-connect benchmark to fork a new process for the TLS server,
so that the store server in master process does not interfere with the
benchmarking client.

Added more configuration options to the benchmark:
- protocol (default, SSLv3_method, etc.)
- number of cluster workers

Simplified the default combination of options.
README: client configuration, performance

Added a section on how to correctly configure node's TLS client.

Removed Benchmarking section, added a new section on performance and how
difficult it is to predict possible gains.
fixup! fixed README after code review
fixup! another fix in README