Add warm-up connection to connectivity tests
For reasons beyond me, one connection (out of many) for the BOSH connectivity test seems to fail - but only on the infrastructure for Github Actions.
From the output, it appears to be the _first_ connection that fails. I suspect that this is triggered by a weird scheduling/timing/eventing thingy that is specific to that environment.
This commit adds an additional connection attempt, for which the outcome will be ignored. Hopefully by 'warming up' the system under test, we get more stable results.
Identify docker hub pushes for non-released code as 'alpha'
Openfire builds that are not a release typically identify themselves as 'alpha'. The corresponding Docker images could do the same, which would reduce confusion.
Docker publishing only after all tests succeed.
Previously, only the Smack test outcome was taken into account (as the others were not stable). Smack's output was not very stable either, which made this seemingly an arbitrary choice. The resulting flow diagram might have added more confusion than worked around actual issues?
