The (*Environment).Activate method only guarded against multiple calls
and therefore wasn't properly re-entrant.
If a plugin calls an UpdateConfiguration in the OnActivate hook, it would
again call this method, resulting in 2 plugin processes getting created.
To prevent that from happening, we pre-emptively set the status to running
just after the supervisor is created.
I am not sure why starting the plugin normally from the server does not
cause this because the root cause is the same and there should be 2 plugin
processes created in the normal scenario as well. I have not spent time
looking into that. But let me know if you want me to.
Unit test: This might be a bit hard to test via a unit test. I think
an e2e test maybe written in the playbooks test itself which counts
the number of processes that the server spawns.
https://mattermost.atlassian.net/browse/MM-44045
```release-note
NONE
```
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