threadgroup: use threading rather than greenthread

Since threading is monkey patched in case we use eventlet, this is
change is a no-op. It buys use less usage of eventlet modules in the
end.

Change-Id: I7d39eb71b47ec00ed1c1256d94cfd4de80e3bdd5
default connectionpool to WARN log level

requests.packages.urllib3.connectionpool issues an INFO log message
every time a new connection is added to the pool. While this may
be incredibly interesting to the authors of the requests package,
to an OpenStack operator this is just log spam.

set the default for this logger to WARN to tighten up the logs so
that INFO level is meaningful.

Change-Id: Icb30afe569ba80d1d322ef7f22a46a3e60b3ba9a
Merge "threadgroup: use threading rather than greenthread"
Merge "default connectionpool to WARN log level"