simple-init: default to NetworkManager for CentOS and Fedora

NetworkManager with simple-init has proven to be stable in OpenStack
infra, switch to it by default for CentOS and Fedora.  For CentOS 8
and Fedora, add a check to make it the only option.  Thus only CenOS 7
remains optionally using the legacy scripts; this is likely not used
anywhere (infra is really the primary user, where NetworkManager is
already used); we can likely remove this variable (and hence path) in
a future cleanup.

In the setup, remove rhel7 element which was never really tested.
Reorganise the fallthrough to call out the default paths as doing
nothing.

Change-Id: Ic996956da4b85f7d95179b8df9881d5f52c091af

.zuul.d/jobs.yaml

@@ -223,8 +223,6 @@
         base_element: centos-minimal
         release: '7'
         mirror: "http://{{ zuul_site_mirror_fqdn }}/centos"
-        env-vars:
-          DIB_SIMPLE_INIT_NETWORKMANAGER: '1'
 
 - job:
     name: dib-nodepool-functional-openstack-fedora-29-src
@@ -238,8 +236,6 @@
       nodepool_diskimage:
         base_element: fedora-minimal
         release: '29'
-        env-vars:
-          DIB_SIMPLE_INIT_NETWORKMANAGER: '1'
 
 - job:
     name: dib-nodepool-functional-openstack-fedora-30-src
@@ -253,8 +249,6 @@
       nodepool_diskimage:
         base_element: fedora-minimal
         release: '30'
-        env-vars:
-          DIB_SIMPLE_INIT_NETWORKMANAGER: '1'
 
 - job:
     name: dib-nodepool-functional-openstack-ubuntu-trusty-src

diskimage_builder/elements/simple-init/environment.d/15-simple-init-networkmanager

@@ -1 +1,12 @@
+if [[ ${DISTRO_NAME} =~ (centos|fedora) ]]; then
+    export DIB_SIMPLE_INIT_NETWORKMANAGER=${DIB_SIMPLE_INIT_NETWORKMANAGER:-1}
+else
     export DIB_SIMPLE_INIT_NETWORKMANAGER=${DIB_SIMPLE_INIT_NETWORKMANAGER:-0}
+fi
+
+if [[ ${DISTRO_NAME} == "centos" && $DIB_RELEASE -ge 8 ]] || [[ ${DISTRO_NAME} == "fedora" ]]; then
+    if [[ $DIB_SIMPLE_INIT_NETWORKMANAGER == 0 ]]; then
+        echo "simple-init only supports NetworkManager mode on Fedora and CentOS 8"
+        exit 1
+    fi
+fi

diskimage_builder/elements/simple-init/post-install.d/80-simple-init

@@ -12,7 +12,7 @@ case "$DIB_INIT_SYSTEM" in
         exit 0
         ;;
     systemd)
-        if [[ ${DISTRO_NAME} =~ (centos|rhel7|fedora) ]]; then
+        if [[ ${DISTRO_NAME} == centos && ${DIB_RELEASE} -eq 7 ]]; then
             if [[ ${DIB_SIMPLE_INIT_NETWORKMANAGER} != 1 ]]; then
                 # NOTE(pabelanger): Glean requires network.service for
                 # these platforms when not using networkmanager
@@ -22,6 +22,10 @@ case "$DIB_INIT_SYSTEM" in
             # on suse, this is named wicked.service, but it's the same
             # as network.service.
             systemctl enable wicked.service
+        else
+            # NOTE(ianw): it might be better to whitelist platforms in
+            # the future, but for now assume it will "just work"
+            continue
         fi
         ;;
     openrc)

releasenotes/notes/simple-init-nm-5d19e249c0a4560b.yaml

@@ -0,0 +1,6 @@
+---
+upgrade:
+  - |
+    The ``simple-init`` element will now default to using NetworkManager
+    for CentOS and Fedora platforms.  For CentOS 8 and Fedora, the
+    ``DIB_SIMPLE_INIT_NETWORKMANAGER=0`` option is no longer supported.