Test bootstrap-os on more platforms (#6277)

roles/bootstrap-os/molecule/default/molecule.yml

@@ -10,6 +10,10 @@ driver:
   provider:
     name: libvirt
 platforms:
+  - name: ubuntu16
+    box: generic/ubuntu1604
+    cpus: 1
+    memory: 512
   - name: ubuntu18
     box: generic/ubuntu1804
     cpus: 1
@@ -18,6 +22,18 @@ platforms:
     box: generic/ubuntu2004
     cpus: 1
     memory: 512
+  - name: centos7
+    box: centos/7
+    cpus: 1
+    memory: 512
+  - name: debian9
+    box: generic/debian9
+    cpus: 1
+    memory: 512
+  - name: debian10
+    box: generic/debian10
+    cpus: 1
+    memory: 512
 provisioner:
   name: ansible
   lint: