Integration tests set up and publish descriptors for an exit relay

Some support for talking with Tor's ORPort has recently made it to stem (see #18856 (closed)).

Integration tests thus needed to set up a relay with ORPort in the torrc. 3fe2221ae2bad6d826c05fd0ce96e5c09a21fc01 did this, but the defaults for a relay are to publish descriptors and act as an exit. Both of these are undesirable for stem's integration tests.

The corresponding torrc options to disable these are:

ExitRelay 0
PublishServerDescriptor 0

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