Does not install behind a proxy

I have a juju2 model whose applications have to use a proxy to reach the internet.

Most charms work ok, but elasticsearch seems to ignore the juju proxy settings and doesn't work:

2017-02-17 12:07:13 INFO juju-log Installing ansible with options: ['--option=Dpkg::Options::=--force-confold']
2017-02-17 12:07:13 INFO install Reading package lists...
2017-02-17 12:07:13 INFO install Building dependency tree...
2017-02-17 12:07:13 INFO install Reading state information...
2017-02-17 12:07:13 INFO install ansible is already the newest version.
2017-02-17 12:07:13 INFO install The following packages were automatically installed and are no longer required:
2017-02-17 12:07:13 INFO install libfreetype6 os-prober
2017-02-17 12:07:13 INFO install Use 'apt-get autoremove' to remove them.
2017-02-17 12:07:13 INFO install 0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
2017-02-17 12:07:13 INFO juju-log /usr/bin/rsync -r --delete --executability ansible_module_backports /usr/share/ansible
2017-02-17 12:07:14 INFO install
2017-02-17 12:07:14 INFO install PLAY [localhost] **************************************************************
2017-02-17 12:07:14 INFO install
2017-02-17 12:07:14 INFO install GATHERING FACTS ***************************************************************
2017-02-17 12:07:15 INFO install ok: [localhost]
2017-02-17 12:07:15 INFO install
2017-02-17 12:07:15 INFO install TASK: [Add apt key.] **********************************************************
2017-02-17 12:07:46 INFO install failed: [localhost] => {"failed": true, "item": "", "traceback": "Traceback (most recent call last):\n File \"/.ansible/tmp/ansible-tmp-1487333235.43-207024382735290/apt_key\", line 144, in download_key\n return rsp.read()\nAttributeError: 'NoneType' object has no attribute 'read'\n"}
2017-02-17 12:07:46 INFO install msg: error getting key id from url
2017-02-17 12:07:46 INFO install
2017-02-17 12:07:46 INFO install FATAL: all hosts have already failed -- aborting
2017-02-17 12:07:46 INFO install
2017-02-17 12:07:46 INFO install PLAY RECAP ********************************************************************
2017-02-17 12:07:46 INFO install localhost : ok=1 changed=0 unreachable=0 failed=1
2017-02-17 12:07:46 INFO install
2017-02-17 12:07:46 INFO install Traceback (most recent call last):
2017-02-17 12:07:46 INFO install File "/var/lib/juju/agents/unit-elasticsearch-0/charm/hooks/install", line 101, in <module>
2017-02-17 12:07:46 INFO install hooks.execute(sys.argv)
2017-02-17 12:07:46 INFO install File "/var/lib/juju/agents/unit-elasticsearch-0/charm/hooks/charmhelpers/contrib/ansible/__init__.py", line 171, in execute
2017-02-17 12:07:46 INFO install self.playbook_path, tags=[hook_name])
2017-02-17 12:07:46 INFO install File "/var/lib/juju/agents/unit-elasticsearch-0/charm/hooks/charmhelpers/contrib/ansible/__init__.py", line 116, in apply_playbook
2017-02-17 12:07:46 INFO install subprocess.check_call(call, env=env)
2017-02-17 12:07:46 INFO install File "/usr/lib/python2.7/subprocess.py", line 540, in check_call
2017-02-17 12:07:46 INFO install raise CalledProcessError(retcode, cmd)
2017-02-17 12:07:46 INFO install subprocess.CalledProcessError: Command '['ansible-playbook', '-c', 'local', 'playbook.yaml', '--tags', 'install']' returned non-zero exit status 2
2017-02-17 12:07:46 ERROR juju.worker.uniter.operation runhook.go:107 hook "install" failed: exit status 1

And indeed:
# netstat -anp 2>/dev/null|grep SYN
tcp 0 1 10.245.204.158:48610 23.21.141.126:80 SYN_SENT 3282/python

$ juju model-config|grep -i proxy
apt-ftp-proxy default ""
apt-http-proxy default ""
apt-https-proxy default ""
ftp-proxy default ""
http-proxy controller http://squid.vmwarestack:3128/
https-proxy controller http://squid.vmwarestack:3128/
no-proxy controller localhost,127.0.0.1,10.245.200.25,169.254.169.254,10.245.200.27
proxy-ssh default false

on the elasticsearch/0 unit:
# cat /home/ubuntu/.juju-proxy
export http_proxy=http://squid.vmwarestack:3128/
export HTTP_PROXY=http://squid.vmwarestack:3128/
export https_proxy=http://squid.vmwarestack:3128/
export HTTPS_PROXY=http://squid.vmwarestack:3128/
export no_proxy=10.245.200.25,10.245.200.27,10.245.204.111,127.0.0.1,169.254.169.254,::1,localhost
export NO_PROXY=10.245.200.25,10.245.200.27,10.245.204.111,127.0.0.1,169.254.169.254,::1,localhost

I even copied that to /etc/environment, but didn't help.

apt has the right proxy settings over there:
root@juju-ce7091-25-lxd-0:/etc/apt# grep proxy -ri .
./apt.conf.d/42-juju-proxy-settings:Acquire::http::Proxy "http://squid.vmwarestack:3128/";
./apt.conf.d/42-juju-proxy-settings:Acquire::https::Proxy "http://squid.vmwarestack:3128/";

Maybe the charm needs to grow a specific proxy option.