This uses the new 'prlimit' parameter for oslo.concurrency execute
method, to set an address space limit of 1GB and CPU time limit
of 2 seconds, when running qemu-img.
This is a re-implementation of the previously reverted commit
commit da217205f53f9a38a573fb151898fbbeae41021d
Author: Tristan Cacqueray <tdecacqu@redhat.com>
Date: Wed Aug 5 17:17:04 2015 +0000
virt: Use preexec_fn to ulimit qemu-img info call
Closes-Bug: #1449062
Change-Id: I135b5242af1bfdcb0ea09a6fcda21fc03a6fbe7d