Get unix_sock_group & config_sys as an option

- unix_sock_group: libvirt 3.x from UCA repo by default uses
  "libvirt" group for socket ownership, so get the name
  of the group from pillar if given.
- config_sys: handle sysconfig file location
  defined in parameters.

Change-Id: I06dd3707efc191a81af1cf60d8dbeef4e9ea5964
diff --git a/README.rst b/README.rst
index 7748e87..c94bb69 100644
--- a/README.rst
+++ b/README.rst
@@ -14,6 +14,7 @@
     libvirt:
       server:
         enabled: true
+        unix_sock_group: libvirt
         virtualizations:
         - kvm
         network: