AVRO-4185: [C++] Use a temp file in StreamTests

[gahr]

What is the purpose of the change

StreamTests uses the test_str.bin file. This is problematic in our setup because we build and test 32-bit and 64-bit versions in parallel. When the 32-bit and 64-bit StreamTest happen to run concurrently, one ends up deleting the file that the other is trying to read.

My solution here is to use a temporary file instead of the hard-coded test_str.bin.

This fixes AVRO-4185.

Verifying this change

This change is already covered by existing tests, such as StreamTests.

Documentation

• Does this pull request introduce a new feature? (no)