test: Add more time to spawn praefect

What does this MR do and why?

Quite some test jobs failed because the praefect can't be connected. See gitaly#6196 (closed).

Our current observations are:

1. The praefect process is spawned, and pid is not nil.
2. The current timeout is 20s. The failed testing jobs timed out and dropped connection to praefect before praefect could take any request, that is why the `log/praefect-test.log" is empty.

This commit adds a private method process_details(). We use the method to print the process status before sending termination signal to the process. It is used to determine why praefect is not ready for connecting.

We also added a longer timeout before dropping praefect connection.

This may not certainly fix gitaly#6196 (closed), but it at least can give us more information about the praefect process when the error happens again.

Close gitaly#6196 (closed)

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