base: enable 'opstools' repo on AArch64/CentOS
base: enable 'opstools' repo on AArch64/CentOS

To build 'fluentd' image we need to have 'opstools' repo enabled.

On x86-64 it is enabled by installing proper centos-release-opstools
package but this option is not available (yet) for aarch64.

Change-Id: I4b49270a2e0781431e22dc411774e4c6440045d9

openstack/kolla,stackforge/kolla,rahulunair/kolla,mrangana/kolla,mrangana/kolla,nihilifer/kolla,stackforge/kolla,openstack/kolla,nihilifer/kolla,rahulunair/kolla,stackforge/kolla