Total of four cases:  The only success case is (2.b), refer below.


(1.a) `systemctl` + 'restart' of 'libvirt-bin':
      /var/run/libvirt/libvirt-sock is NOT created.

(1.b) `service` + 'restart' of 'libvirt-bin':
      /var/run/libvirt/libvirt-sock is NOT created.

(2.a) `systemctl` with 'stop' followed by 'start' of 'libvirt-bin':
      /var/run/libvirt/libvirt-sock is NOT created.

(2.b) `service` with 'stop' followed by 'start' of 'libvirt-bin':
      /var/run/libvirt/libvirt-sock is SUCCESSFULLY created.


=== Verbose ===

(1) Behavior of `service` and `systemctl` with 'restart'
========================================================

The /var/run/libvirt/libvirt-sock is not created at all in either cases.

(1.a) `systemctl` + 'restart' of 'libvirt-bin':
----------
$ sudo systemctl restart libvirt-bin
---
$ file /var/run/libvirt/libvirt-sock
/var/run/libvirt/libvirt-sock: cannot open `/var/run/libvirt/libvirt-sock' (No such file or directory)
---
$ systemctl status libvirt-bin
* libvirt-bin.service - Virtualization daemon
   Loaded: loaded (/lib/systemd/system/libvirt-bin.service; enabled; vendor preset: enabled)
   Active: active (running) since Fri 2016-05-20 06:09:31 EDT; 5s ago
     Docs: man:libvirtd(8)
           http://libvirt.org
 Main PID: 1394 (libvirtd)
    Tasks: 16
   CGroup: /system.slice/libvirt-bin.service
           `-1394 /usr/sbin/libvirtd
----------

(1.b) `service` + 'restart' of 'libvirt-bin':
----------
$ sudo service libvirt-bin restart
---
$ file /var/run/libvirt/libvirt-sock
/var/run/libvirt/libvirt-sock: cannot open `/var/run/libvirt/libvirt-sock' (No such file or directory)
---
$ service libvirt-bin status
* libvirt-bin.service - Virtualization daemon
   Loaded: loaded (/lib/systemd/system/libvirt-bin.service; enabled; vendor preset: enabled)
   Active: active (running) since Fri 2016-05-20 06:10:50 EDT; 12s ago
     Docs: man:libvirtd(8)
           http://libvirt.org
 Main PID: 1437 (libvirtd)
    Tasks: 16
   CGroup: /system.slice/libvirt-bin.service
           `-1437 /usr/sbin/libvirtd
----------



(2) Behavior of `service` and `systemctl` with 'stop' followed by 'start'
=========================================================================

(2.a) `systemctl` with 'stop' followed by 'start' of 'libvirt-bin':
----------
$ sudo systemctl stop libvirt-bin && sudo systemctl start libvirt-bin 
Warning: Stopping libvirt-bin.service, but it can still be activated by:
  libvirt-bin.socket
---
kashyapc@ubuntu-xenial:~/src$ file /var/run/libvirt/libvirt-sock
/var/run/libvirt/libvirt-sock: cannot open `/var/run/libvirt/libvirt-sock' (No such file or directory)
---
kashyapc@ubuntu-xenial:~/src$ systemctl status libvirt-bin
* libvirt-bin.service - Virtualization daemon
   Loaded: loaded (/lib/systemd/system/libvirt-bin.service; enabled; vendor preset: enabled)
   Active: active (running) since Fri 2016-05-20 06:13:44 EDT; 4s ago
     Docs: man:libvirtd(8)
           http://libvirt.org
 Main PID: 1482 (libvirtd)
    Tasks: 16
   CGroup: /system.slice/libvirt-bin.service
           `-1482 /usr/sbin/libvirtd
----------

(2.b) `service` with 'stop' followed by 'start' of 'libvirt-bin':
----------
$ sudo service libvirt-bin stop && sudo service libvirt-bin start
---
$ file /var/run/libvirt/libvirt-sock
/var/run/libvirt/libvirt-sock: socket
---
$ service libvirt-bin status
* libvirt-bin.service - Virtualization daemon
   Loaded: loaded (/lib/systemd/system/libvirt-bin.service; enabled; vendor preset: enabled)
   Active: active (running) since Fri 2016-05-20 06:16:14 EDT; 11s ago
     Docs: man:libvirtd(8)
           http://libvirt.org
 Main PID: 1573 (libvirtd)
    Tasks: 16
   CGroup: /system.slice/libvirt-bin.service
           `-1573 /usr/sbin/libvirtd
----------


Version info
============

$ dpkg -s libvirt-bin | grep Version
Version: 1.3.1-1ubuntu10

$ dpkg -s qemu-kvm | grep Version
Version: 1:2.5+dfsg-5ubuntu10.1