Fix flaky gclient_smoketest.
Fix flaky gclient_smoketest.

It assumed, incorrectly, that git always listens on port 20000.
It's mostly true, except when tests are ran in parallel.

Example of flake: https://logs.chromium.org/logs/infra/buildbucket/cr-buildbucket.appspot.com/8912524891032998560/+/steps/presubmit/0/stdout

R=smut

Recipe-Nontrivial-Roll: build
Change-Id: I96825175e2f899bce703443b80b71bba5953ac72
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1629745
Commit-Queue: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@chromium.org>
Reviewed-by: smut <95deb7aa15d4c615299e47e7688551456568b1fb@google.com>
Auto-Submit: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools