fixed order of install pkg, then set up /etc/default/lxc

works around this error

Setting up lxc (0.7.5-3ubuntu67) ...

Configuration file `/etc/default/lxc'
 ==> File on system created by you or by a script.
 ==> File also in package provided by package maintainer.
   What would you like to do about it ?  Your options are:
    Y or I  : install the package maintainer's version
    N or O  : keep your currently-installed version
      D     : show the differences between the versions
      Z     : start a shell to examine the situation
 The default action is to keep your current version.
*** lxc (Y/I/N/O/D/Z) [default=N] ? 
invoke-rc.d: policy-rc.d denied execution of start.
lxc-net start/running