$ lxc launch ubuntu:xenial lp1570356
Creating lp1570356
Starting lp1570356

$ lxc exec lp1570356 bash
root@lp1570356:~#

root@lp1570356:~# apt install barbican-api 

... 

root@lp1570356:~# dpkg -l 'barbican*'
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name                                                    Version                          Architecture                     Description
+++-=======================================================-================================-================================-====================================================================================================================
ii  barbican-api                                            1:2.0.0-0ubuntu1                 all                              OpenStack Key Management Service - API Server
ii  barbican-common                                         1:2.0.0-0ubuntu1                 all                              OpenStack Key Management Service - common files


root@lp1570356:~# python
Python 2.7.12 (default, Nov 19 2016, 06:48:10) 
[GCC 5.4.0 20160609] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import barbican.plugin.interface.certificate_manager
Option "verbose" from group "DEFAULT" is deprecated for removal.  Its value may be silently ignored in the future.
Could not load 'simple_certificate_event': cannot import name certificate_manager
cannot import name certificate_manager
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/stevedore/extension.py", line 163, in _load_plugins
    verify_requirements,
  File "/usr/lib/python2.7/dist-packages/stevedore/named.py", line 123, in _load_one_plugin
    verify_requirements,
  File "/usr/lib/python2.7/dist-packages/stevedore/extension.py", line 184, in _load_one_plugin
    plugin = ep.resolve()
  File "/usr/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 2235, in resolve
    module = __import__(self.module_name, fromlist=['__name__'], level=0)
  File "/usr/lib/python2.7/dist-packages/barbican/plugin/simple_certificate_manager.py", line 19, in <module>
    from barbican.plugin.interface import certificate_manager as cert
ImportError: cannot import name certificate_manager

root@lp1570356:~# echo 'deb http://archive.ubuntu.com/ubuntu/ xenial-proposed restricted main multiverse universe' >> /etc/apt/sources.list
root@lp1570356:~# sudo apt update
Get:1 http://security.ubuntu.com/ubuntu xenial-security InRelease [102 kB]
Hit:2 http://archive.ubuntu.com/ubuntu xenial InRelease  
Get:3 http://archive.ubuntu.com/ubuntu xenial-updates InRelease [102 kB]           
Get:4 http://archive.ubuntu.com/ubuntu xenial-backports InRelease [102 kB]                     
Get:5 http://archive.ubuntu.com/ubuntu xenial-proposed InRelease [253 kB]
Get:6 http://archive.ubuntu.com/ubuntu xenial-proposed/main amd64 Packages [104 kB]
Get:7 http://archive.ubuntu.com/ubuntu xenial-proposed/main Translation-en [36,8 kB]
Get:8 http://archive.ubuntu.com/ubuntu xenial-proposed/multiverse amd64 Packages [1 024 B]
Get:9 http://archive.ubuntu.com/ubuntu xenial-proposed/multiverse Translation-en [784 B]
Get:10 http://archive.ubuntu.com/ubuntu xenial-proposed/universe amd64 Packages [48,1 kB]
Get:11 http://archive.ubuntu.com/ubuntu xenial-proposed/universe Translation-en [16,9 kB]
Fetched 768 kB in 1s (492 kB/s)             
Reading package lists... Done
Building dependency tree       
Reading state information... Done
19 packages can be upgraded. Run 'apt list --upgradable' to see them.
root@lp1570356:~# sudo apt upgrade
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Calculating upgrade... Done
The following package was automatically installed and is no longer required:
  snap-confine
Use 'sudo apt autoremove' to remove it.
The following packages will be upgraded:
  barbican-api barbican-common coreutils init init-system-helpers libpam-systemd libpci3 libsystemd0 libudev1 mdadm pciutils python-barbican snap-confine snapd systemd systemd-sysv ubuntu-core-launcher udev zlib1g
19 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 16,6 MB of archives.
After this operation, 1 574 kB of additional disk space will be used.
Do you want to continue? [Y/n] 

...

Get:17 http://archive.ubuntu.com/ubuntu xenial-proposed/universe amd64 barbican-api all 1:2.0.0-0ubuntu1.1 [2 734 B]                                                                                                                                  
Get:18 http://archive.ubuntu.com/ubuntu xenial-proposed/universe amd64 barbican-common all 1:2.0.0-0ubuntu1.1 [10,4 kB]                                                                                                                               
Get:19 http://archive.ubuntu.com/ubuntu xenial-proposed/universe amd64 python-barbican all 1:2.0.0-0ubuntu1.1 [226 kB]                                                                                                                                

...

root@lp1570356:~# python
>>> import barbican.plugin.interface.certificate_manager
Option "verbose" from group "DEFAULT" is deprecated for removal.  Its value may be silently ignored in the future.
>>>