fix: hold assigned port at start-up until Pg start command exec

[tzemanovic]

Hi,

Thanks for this crate! I'm using multiple embedded DBs concurrently with auto-assigned ports and it seems that there is a race condition in the start-up as randomly they fail to start. I found that the assigned port at start-up is not held open before the pg_ctl command uses it again, so another process may try re-use it in the meantime.

This fix instead tries to assign a random port directly for the pg_ctl command and retry 3 times on port conflict

[brianheineman]

Hello @tzemanovic, thank you for the pull request. Instead of randomly assigning the port, my preference would be to get an ephemeral port from the OS and add support for retrying (with a configurable retry) when a port bind failure occurs.

[tzemanovic]

Hello @tzemanovic, thank you for the pull request. Instead of randomly assigning the port, my preference would be to get an ephemeral port from the OS and add support for retrying (with a configurable retry) when a port bind failure occurs.

I've made the changes, thanks @brianheineman !