Add the processutils from oslo-incubator.

This is a module specific add rather than a full sync. The processutils
module will be used to determine the default number of workers for keystone
running under eventlet.

Processutils sync'd from oslo commit hash 6a60f84258

Change-Id: I6cbca7d54ca97cce962d3cc1131388840ddf9a7c
Related-Bug: #1371154
Merge "Add the processutils from oslo-incubator."