* Handpick cluster cipher suites when they're not user-set
There is an undocumented way for users to choose cluster cipher suites
but for the most part this is to paper over the fact that there are
undesirable suites in TLS 1.2.
If not explicitly set, have the set of cipher suites for the cluster
port come from a hand-picked list; either the allowed TLS 1.3 set (for
forwards compatibility) or the three identical ones for TLS 1.2.
The 1.2 suites have been supported in Go until at least as far back as
Go 1.9 from two years ago. As a result in cases where no specific suites
have been chosen this _ought_ to have no compatibility issues.
Also includes a useful test script.
