The new nanobench benchmarking framework introduced in Dxxxx has no
built-in output format compatible with Teamcity. But since it provides a
very complete json output, it is easy to parse it and generate the
messages we want for teamcity.
This diff makes the bench-bitcoin target generate csv and json output
files, and adds a simple python script to parse the json output and send
teamcity messages when run on CI.
Depends on D9226.