(SIMP-10204) Ensure testing with CentOS 8.4 (#83)

- update the EL8 nodes in the acceptance tests
  to run with generic/centos8 to make sure they using
  CentOS 8.4
- update oel7 node to generic box from onyxpoint

SIMP-10204 #comment update rsync
SIMP-10239 #close

spec/acceptance/nodesets/default.yml

@@ -12,7 +12,7 @@ HOSTS:
       - master
       - client
     platform: el-8-x86_64
-    box: centos/8
+    box: generic/centos8
     hypervisor: <%= hypervisor %>
 
   el7:

spec/acceptance/nodesets/oel.yml

@@ -19,7 +19,7 @@ HOSTS:
     roles:
       - client
     platform: el-7-x86_64
-    box: onyxpoint/oel-7-x86_64
+    box: generic/oracle7
     hypervisor: <%= hypervisor %>
 
 CONFIG: