Two runs of the same job on the same patch can yield quite different
numbers for API calls if we just count the raw calls. Many of these
are tempest polling for resources, which on a slow worker can require
many more calls than a fast one.
Tempest seems to not change its User-Agent string, but the client
libraries do. So, if we ignore the regular "python-urllib" agent
calls, we get a much more stable count of service-to-service API
calls in the performance report.
Note that we were also logging in a different (less-rich) format for
the tls-proxy.log file, which hampers our ability to parse that
data in the same format. This switches it to "combined" which is used
by the access.log and contains more useful information, like the
user-agent, among other things.
Change-Id: I8889c2e53f85c41150e1245dcbe2a79bac702aad
64d68679d9