chore: allow custom port in samples tests

[DominicKramer]

This allows multiple runs of the samples tests to occur on the
same machine at the same time to test for conflicts between
concurrently running tests.

[JustinBeckwith]

How will this actually help us in the tests? Seems like it would be better to have the quickstart main method accept the port as a command line arg, then choose a high order random port in the test to pass to the sample. I don't think we want to use an env var here.

[codecov]

Codecov Report

Merging #272 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #272   +/-   ##
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  Coverage   94.87%   94.87%           
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  Files           2        2           
  Lines          78       78           
  Branches        8        8           
=======================================
  Hits           74       74           
  Misses          4        4

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[kjin]

@JustinBeckwith For the record, I think this is a pretty standard thing to do that I've seen in other samples (using env var).

[DominicKramer]

@JustinBeckwith I'm fine using an env var or as a program argument. This PR itself doesn't fix any issues in the test. However, when trying them locally it is nice to have multiple instance running concurrently to test for issues. Having the port adjustable makes that easier.

[JustinBeckwith]

Got it. If the goal is to make the tests more reliable, this isn't gonna help. But if the goal was just allow setting the port locally, LGTM.