Comment 5 for bug 1687129

Here is a run with the updated unattended-upgrades package against the staging version of the ESM service which is using the requested changes to the Release file. It recognises the sample landscape-common update that is there:

root@precise-esm:~# unattended-upgrades --dry-run -d 2>&1
Initial blacklisted packages:
Starting unattended upgrades script
Allowed origins are: ['o=Ubuntu,a=precise-security', 'o=UbuntuESM,a=precise']
Checking: landscape-common (["<Origin component:'main' archive:'precise' origin:'UbuntuESM' label:'UbuntuESM' site:'extended.security.staging.ubuntu.com' isTrusted:True>"])
pkgs that look like they should be upgraded: landscape-common
Fetched 0 B in 0s (0 B/s)
<apt_pkg.AcquireItem object:Status: 2 Complete: 1 Local: 1 IsTrusted: 1 FileSize: 224960 DestFile:'/var/cache/apt/archives/landscape-common_14.12-0ubuntu5.12.04_amd64.deb' DescURI: 'https://user:<email address hidden>/ubuntu/pool/main/l/landscape-client/landscape-common_14.12-0ubuntu5.12.04_amd64.deb' ID:0 ErrorText: ''>
check_conffile_prompt('/var/cache/apt/archives/landscape-common_14.12-0ubuntu5.12.04_amd64.deb')
found pkg: landscape-common
blacklist: []
InstCount=1 DelCount=0 BrokenCout=0
Option --dry-run given, *not* performing real actions
Packages that are upgraded: landscape-common
Writing dpkg log to '/var/log/unattended-upgrades/unattended-upgrades-dpkg_2017-05-03_16:49:57.997981.log'
Preconfiguring packages ...
/usr/bin/dpkg --status-fd 6 --unpack --auto-deconfigure /var/cache/apt/archives/landscape-common_14.12-0ubuntu5.12.04_amd64.deb
/usr/bin/dpkg --status-fd 8 --configure landscape-common:amd64
All upgrades installed
InstCount=1 DelCount=0 BrokenCount=0

root@precise-esm:~# apt-cache policy unattended-upgrades
unattended-upgrades:
  Installed: 0.76ubuntu1.3
  Candidate: 0.76ubuntu1.3
  Version table:
 *** 0.76ubuntu1.3 0
        500 http://br.archive.ubuntu.com/ubuntu/ precise-proposed/main amd64 Packages

With the previous version of unattended-upgrades (0.76ubuntu1.2), the ESM staging archive isn't recognized:
root@precise-esm:~# unattended-upgrades --dry-run -d 2>&1
Initial blacklisted packages:
Starting unattended upgrades script
Allowed origins are: ['o=Ubuntu,a=precise-security']
adjusting candidate version: '<Version: package:'unattended-upgrades' version:'0.76ubuntu1.1'>'
Checking: landscape-common (["<Origin component:'main' archive:'precise' origin:'UbuntuESM' label:'UbuntuESM' site:'extended.security.staging.ubuntu.com' isTrusted:True>"])
pkgs that look like they should be upgraded:
Fetched 0 B in 0s (0 B/s)
blacklist: []
InstCount=0 DelCount=0 BrokenCout=0
No packages found that can be upgraded unattended and no pending auto-removals