[Upgrade] Upgrade script hangs on write to log operation

[Tatyanka]

Note, there is no 100% steps to reproduce and I was faced with this 2 times from 20 attempts

Steps to reproduce:
1. Download to the master node upgrade archive
2. Extract data to the /var/tmp directory
3. invoke upgrade script:
chmod 755 upgrade.sh
sudo -S bash -c upgrade.sh

Expected Result:
Upgrade pass, script finish, there is no upgrade script pid in psafuxxw| grep upgrade command output

Actual Result:
Upgrade was success. Containers are in Running state, but script is not ended it works more the 72 hours (It stall on write data in log file)
 ps uax| grep upgrade
root 17944 0.0 0.0 106064 672 ? Ss Jun27 0:00 /bin/bash /var/tmp/update/upgrade.sh
root 18016 0.0 1.5 239548 24552 ? S Jun27 0:01 python /var/tmp/update/upgrade/bin/fuel-upgrade --src /var/tmp/update/upgrade docker openstack

starce show
write(2, "2014-06-27 15:51:26 DEBUG 18016 "..., 91ce says :

Also a piece of info from Eugene L
http://paste.openstack.org/show/85208/

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/103844

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/103844
Committed: https://git.openstack.org/cgit/stackforge/fuel-web/commit/?id=de99bc12e5fc614180a39c7428bc7a40ae81f264
Submitter: Jenkins
Branch: master

commit de99bc12e5fc614180a39c7428bc7a40ae81f264
Author: Evgeniy L <email address hidden>
Date: Tue Jul 1 15:02:03 2014 +0400

    Upgrade, enable stdout log only if pseudo-tty is enabled

    When user runs fuel upgrade script in no-tty mode
    and then closes stdout (for example suspends ^Z the process),
    during some time (i.e. when buffer is over) it hangs on
    writing to stdout.

    blueprint upgrade-to-5-1
    Closes-bug: #1336218
    Change-Id: I42af9c59e6a5e10645c8e59d13dfa111da53851d

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/5.0
Review: https://review.openstack.org/104164

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/104164
Committed: https://git.openstack.org/cgit/stackforge/fuel-web/commit/?id=3c0920d566a6bc6489ce196d9ff42017a2808a23
Submitter: Jenkins
Branch: stable/5.0

commit 3c0920d566a6bc6489ce196d9ff42017a2808a23
Author: Evgeniy L <email address hidden>
Date: Tue Jul 1 15:02:03 2014 +0400

    Upgrade, enable stdout log only if pseudo-tty is enabled

    When user runs fuel upgrade script in no-tty mode
    and then closes stdout (for example suspends ^Z the process),
    during some time (i.e. when buffer is over) it hangs on
    writing to stdout.

    blueprint upgrade-to-5-0-1
    Closes-bug: #1336218
    Change-Id: I42af9c59e6a5e10645c8e59d13dfa111da53851d