[C++] Complete round trip Union file/stream IPC tests

[asfimport]

I encountered this working on ARROW-459 – while we have the ability to write and read record batches, the schema/metadata parts of the file and stream reader/writer implementations are not complete. I did a bit of work on it in my patch for ARROW-459 but gave up as I realized there was more work to do than made sense for that patch (which is for dictionary-encoded data).

Reporter: Wes McKinney / @wesm
Assignee: Wes McKinney / @wesm

Related issues:

• [Integration] Add integration tests for Union types (blocks)

_{Note: This issue was originally created as ARROW-576. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
PR: #356

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 356
#356