Fix Xenial noninteractive apt installs
Fix Xenial noninteractive apt installs

In Xenial -y is required with DEBIAN_FRONTEND=noninteractive, otherwise
the script prompts for confirmation and aborts because its not reading
from an interactive terminal.

Connects rcbops/u-suk-dev#825

jacobwagner/rpc-openstack,shannonmitchell/rpc-openstack,galstrom21/rpc-openstack,robb-romans/rpc-openstack,hughsaunders/rpc-openstack,cfarquhar/rpc-openstack,prometheanfire/rpc-openstack,rcbops/rpc-openstack,BjoernT/rpc-openstack,hughsaunders/rpc-openstack,mancdaz/rpc-openstack,cfarquhar/rpc-openstack,cloudnull/rpc-openstack,git-harry/rpc-openstack,git-harry/rpc-openstack,robb-romans/rpc-openstack,major/rpc-openstack,BjoernT/rpc-openstack,jacobwagner/rpc-openstack,major/rpc-openstack,shannonmitchell/rpc-openstack,rcbops/rpc-openstack,cloudnull/rpc-openstack,mancdaz/rpc-openstack,prometheanfire/rpc-openstack,galstrom21/rpc-openstack