Use of logging in native thread causes deadlock connecting to libvirtd

When connecting to libvirtd daemon we were calling the _connect
method in a native thread. The use of logging in this method hit this
bug in eventlet https://bitbucket.org/eventlet/eventlet/issue/137/
causing nova-compute to hang.

Closes-Bug: #1252409

Change-Id: I0d22c3ed1b3288aeb1afae130f11a4f38dc6440a
Merge "Use of logging in native thread causes deadlock connecting to libvirtd"