Add centos-7 plain nodes

I'm not quite sure why I didn't add this with the other -plain nodes;
add it for completeness.

Change-Id: Ia14c2733272ea4c108dccef4b5c724769ed22a01

nodepool/nl01.openstack.org.yaml

@@ -44,6 +44,8 @@ labels:
     min-ready: 1
   - name: ubuntu-xenial-plain
     min-ready: 1
+  - name: centos-7-plain
+    min-ready: 1
   - name: centos-8-plain
     min-ready: 1
 
@@ -83,6 +85,8 @@ providers:
         config-drive: true
       - name: ubuntu-xenial-plain
         config-drive: true
+      - name: centos-7-plain
+        config-drive: true
       - name: centos-8-plain
         config-drive: true
     pools:
@@ -159,6 +163,11 @@ providers:
             flavor-name: 'Performance'
             diskimage: ubuntu-xenial-plain
             key-name: infra-root-keys-2020-05-13
+          - name: centos-7-plain
+            min-ram: 8192
+            flavor-name: 'Performance'
+            diskimage: centos-7-plain
+            key-name: infra-root-keys-2020-05-13
           - name: centos-8-plain
             min-ram: 8192
             flavor-name: 'Performance'
@@ -204,4 +213,5 @@ diskimages:
   - name: ubuntu-xenial
   - name: ubuntu-bionic-plain
   - name: ubuntu-xenial-plain
+  - name: centos-7-plain
   - name: centos-8-plain

nodepool/nodepool.yaml

@@ -15,6 +15,8 @@ providers:
     cloud: ovh
     rate: 0.1
     diskimages: &provider_diskimages
+      - name: centos-7-plain
+        config-drive: true
       - name: centos-7
         config-drive: true
       - name: centos-8
@@ -343,6 +345,17 @@ diskimages:
       DIB_DISTRIBUTION_MIRROR: 'http://mirror.dfw.rax.opendev.org/ubuntu'
       DIB_DEBIAN_COMPONENTS: 'main,universe'
 
+  - name: centos-7-plain
+    parent: base
+    pause: false
+    release: '7'
+    elements:
+      - cache-devstack
+      - centos-minimal
+      - epel
+    env-vars:
+      DIB_EPEL_DISABLED: '1'
+
   - name: centos-8-plain
     parent: base
     pause: false