[C++] Install GCS testbench for CI builds

[asfimport]

To continue work on ARROW-1231 I will need to write integration tests for the GCS FileSystem against the GCS testbench. That requires creating a script to install the testbench, and I should write at least one test that uses it.

Reporter: Carlos O'Ryan / @coryan
Assignee: Carlos O'Ryan / @coryan

Related issues:

• [C++] Add filesystem / IO implementation for Google Cloud Storage (is a child of)

PRs and other links:

• GitHub Pull Request #11375

_{Note: This issue was originally created as ARROW-14236. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 11375
#11375