How to handle role requirements on other roles

[Richard Megginson]

Many of our roles need to use the functionality provided by another role.

An example for the Logging role:
* When new certs need to be generated with deploying the logging system,
  integration with the certificate role. See also
  (Certificate README)[
https://github.com/linux-system-roles/certificate/blob/master/README.md]
* A RELP connection may need to open a port in the firewall, and could use
the
  firewall role.
* A RELP connection may need to set SELinux attributes for a port, and
could use
  the selinux role.

There are many more candidates which could use the Certificate role, the
Network
role, the Firewall role, etc.  Any role that needs an X509 cert could use
the
certificate role.  Any role that needs to open a port could use the
firewall and
selinux roles.

I have submitted a proposal at
https://github.com/linux-system-roles/linux-system-roles.github.io/pull/78
please comment