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Hopefully fixed upstream by v1.2.1-11-gfe89b68:

commit fe89b687a02d1a8e1dce695a67b4f9d2c254d7b9
Author: Martin Kletzander <mkletzan>
Date:   Thu Jan 9 07:57:59 2014 +0100

    qemu: Change the default unix monitor timeout

Moving to POST:

http://post-office.corp.redhat.com/archives/rhvirt-patches/2014-April/msg00140.html

It's a tiny fix to update unix monitor timeout from 3 to 30(seconds). Update libvirt to libvirt-0.10.2-32.el6, and following the steps in https://bugzilla.redhat.com/show_bug.cgi?id=892273#c19, domain can start normally.
If change the TIMEOUT in the qemu wrapper to more than 30 seconds, it will fail as expected:
# virsh start rhel6
error: Failed to start domain rhel6
error: internal error Timed out while reading console log output: 

So move bug to VERIFIED.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHBA-2014-1374.html