bootstrap: install network-scripts if EL8
bootstrap: install network-scripts if EL8

network-scripts is required by the network service which is enabled
in tasks/main.yml.
Also run this block of tasks on EL8 only, where it's actually needed.

Change-Id: I2e43de001938bcdec96875ede0ef52d4742dc01c
Closes-bug: 1827277

openstack/tripleo-common,openstack/tripleo-common