play: --no-detach should infer --host=localhost

[oliver-sanders]

In both Cylc 7 & Cylc 8 --host=foo --no-detach is perfectly valid and does what it says on the tin. You will get cylc play running in --no-detach mode over an ssh connection.

However, does this make sense? Should we make --no-detach infer --host=localhost?

Pull requests welcome!

[hjoliver]

I guess it's not much more convenient than actually logging in to the remote host and running cylc play --no-detach there locally, but in what way does it not make sense?

[dpmatthews]

If you specify a remote host via --host then it makes sense to me to use that host. However, what if you don't specify a host but have [scheduler][run hosts] configured? It might make sense to infer --host=localhost in this case rather than run on a remote host.

[oliver-sanders]

(this would be changing the default for this combo rather than necessarily removing the option?)