Determine if GCS ThreadIntegrationTest.ReuseConnections should be kept

This test attempts to measure connection reuse by inspecting curl(Info) log messages. The format of these log messages has changed with recent versions of curl, breaking the test.

Determine if we want to keep this test and if so how to rework the data collection.

Start with GCS ThreadIntegrationTest.ReuseConnections and inspect how it collects curl(Info) log messages. Compare the assumptions in the test with the current curl log format, then determine whether the test should remain; if it does, define a reliable replacement for its data collection and verify the test's connection-reuse measurement.

Written by the indexing model from the issue text.