set close_fds=True in Popen

The current way of using Popen does not close pipes properly,
and therefore long-running keystone processes, which depends on
keystoneclient.common.cms for data sigining, eventually hit
open file limit and stop working. Passing close_fds=True seems
to have solved the problem.

Change-Id: Ife452ab6843c1af5eb39debb8db453e45f78cba9
Closes-Bug: 1382906
Merge "set close_fds=True in Popen"