coverage.py 4.4 removed the path from the filename attribute in its reports.
This leads to incorrect coverage from codecov as it relies on this attribute to
find the source file. Require coverage.py older than version 4.4.
We import the scripts from ycmd with a couple of modifications:
- don't set YCM_CORES=1 as we didn't before, and this makes the build a lot faster
- don't install gcc-4.8 as we didn't before
- install argparse as it is not available in python2.6
The server is multi-threaded and will spawn a new thread for each new request.
Thus, the completers need not manage their own threads or even provide async
APIs; we _want_ them to block because now were implementing the request-response
networking API.
The client gets the async API through the network (i.e., it can do something
else while the request is pending).
