On the current Xenial image, memcached installs fine:

% lxc launch ubuntu-daily:xenial x1
Creating x1
Starting x1
% lxc exec x1 /bin/bash
root@x1:~# apt-get update && apt-get install memcached
Hit:1 http://security.ubuntu.com/ubuntu xenial-security InRelease
Get:2 http://archive.ubuntu.com/ubuntu xenial InRelease [247 kB]
Hit:3 http://archive.ubuntu.com/ubuntu xenial-updates InRelease
Get:4 http://archive.ubuntu.com/ubuntu xenial/main amd64 Packages [1182 kB]
Get:5 http://archive.ubuntu.com/ubuntu xenial/main Translation-en [563 kB]
Get:6 http://archive.ubuntu.com/ubuntu xenial/universe amd64 Packages [7541 kB]
Get:7 http://archive.ubuntu.com/ubuntu xenial/universe Translation-en [4360 kB]
Get:8 http://archive.ubuntu.com/ubuntu xenial/multiverse amd64 Packages [146 kB]                         
Fetched 14.0 MB in 8s (1596 kB/s)                                                                        
Reading package lists... Done
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Suggested packages:
  libcache-memcached-perl libmemcached libanyevent-perl libyaml-perl libterm-readkey-perl
The following NEW packages will be installed:
  memcached
0 upgraded, 1 newly installed, 0 to remove and 3 not upgraded.
Need to get 89.0 kB of archives.
After this operation, 246 kB of additional disk space will be used.
Get:1 http://archive.ubuntu.com/ubuntu xenial/main amd64 memcached amd64 1.4.25-2ubuntu1 [89.0 kB]
Fetched 89.0 kB in 0s (346 kB/s)  
Selecting previously unselected package memcached.
(Reading database ... 25401 files and directories currently installed.)
Preparing to unpack .../memcached_1.4.25-2ubuntu1_amd64.deb ...
Unpacking memcached (1.4.25-2ubuntu1) ...
Processing triggers for ureadahead (0.100.0-19) ...
Processing triggers for systemd (229-4ubuntu4) ...
Processing triggers for man-db (2.7.5-1) ...
Setting up memcached (1.4.25-2ubuntu1) ...
Processing triggers for ureadahead (0.100.0-19) ...
Processing triggers for systemd (229-4ubuntu4) ...
root@x1:~# apt-get -f install
Reading package lists... Done
Building dependency tree       
Reading state information... Done
0 upgraded, 0 newly installed, 0 to remove and 3 not upgraded.


root@x1:~# systemctl status memcached
● memcached.service - memcached daemon
   Loaded: loaded (/lib/systemd/system/memcached.service; enabled; vendor preset: enabled)
   Active: inactive (dead)

root@x1:/lib/systemd/system# grep memcache /etc/group
memcache:x:116:
root@x1:/lib/systemd/system# grep memcache /etc/passwd
memcache:x:112:116:Memcached,,,:/nonexistent:/bin/false

Now, memcached doesn't start cleanly, the following hangs (but starts memcached)

% systemctl start memcached 

Fixing up the systemd service file fixes this (Adding Type=Forking)

# diff -u memcached.service.orig  memcached.service
--- memcached.service.orig	2016-04-19 15:59:31.654599131 +0000
+++ memcached.service	2016-04-19 15:55:34.458022457 +0000
@@ -3,6 +3,7 @@
 After=network.target
 
 [Service]
+Type=Forking
 ExecStart=/usr/share/memcached/scripts/systemd-memcached-wrapper /etc/memcached.conf
 
 [Install]

Then I can systemctl start it just fine

root@x1:~# systemctl start memcached
root@x1:~# systemctl status -l memcached
● memcached.service - memcached daemon
   Loaded: loaded (/lib/systemd/system/memcached.service; enabled; vendor preset: enabled)
   Active: active (running) since Tue 2016-04-19 15:59:57 UTC; 4s ago
 Main PID: 991 (memcached)
    Tasks: 6 (limit: 512)
   Memory: 552.0K
      CPU: 10ms
   CGroup: /system.slice/memcached.service
           └─991 /usr/bin/memcached -m 64 -p 11211 -u memcache -l 127.0.0.1

Apr 19 15:59:57 x1 systemd[1]: Started memcached daemon.