Split overlays into discrete functionality and test

- Closes #987

To make the overlays testable in isolation, and after discussion with
the TSC, removed host/time/source from overlay files.

Signed-off-by: Jonathon Anderson <janderson@ciq.com>

overlays/ifcfg/rootfs/etc/sysconfig/network-scripts/ifcfg.ww

@@ -0,0 +1,40 @@
+{{range $devname, $netdev := .NetDevs -}}
+{{- $filename := print "ifcfg-" $devname ".conf" }}
+{{- file $filename }}
+# This file is autogenerated by warewulf
+TYPE={{ $netdev.Type }}
+DEVICE={{ $netdev.Device }}
+NAME={{ $devname }}
+{{ if $netdev.MTU -}}
+MTU={{ $netdev.MTU }}
+{{ end -}}
+BOOTPROTO=static
+DEVTIMEOUT=10
+IPADDR={{ $netdev.Ipaddr }}
+NETMASK={{ $netdev.Netmask }}
+{{ if $netdev.Gateway -}}
+GATEWAY={{ $netdev.Gateway }}
+{{ end -}}
+{{ if $netdev.Hwaddr -}}
+HWADDR={{ $netdev.Hwaddr }}
+{{ end -}}
+{{ if $netdev.Type -}}
+TYPE={{ $netdev.Type }}
+{{ end -}}
+{{ if $netdev.OnBoot -}}
+ONBOOT={{ $netdev.OnBoot }}
+{{ end -}}
+IPV6INIT=yes
+IPV6_AUTOCONF=yes
+IPV6_DEFROUTE=yes
+IPV6_FAILURE_FATAL=no
+{{ if $netdev.Ipaddr6 -}}
+IPV6ADDR="{{ $netdev.Ipaddr6 }}"
+{{ end -}}
+{{range $tk, $tv := $netdev.Tags -}}
+{{ $prefix := substr 0 3 $tk -}}
+{{ if eq $prefix "DNS" -}}
+{{ $tk }}={{ $tv }}
+{{ end -}}
+{{ end -}}
+{{ end -}}