Add integration test case to explicitly check for optional validity buffer

[asfimport]

When the null count of a Field is 0 the validity buffer is optional in a RecordBatch message. From ARROW-1476, integration tests were failing because of this (see discussion here #1316 (comment)). The failure occurred due to chance of the random seed for generating the validity buffer. We should explicitly test this case for integration testing in the future.

Reporter: Bryan Cutler / @BryanCutler
Assignee: Bryan Cutler / @BryanCutler

PRs and other links:

• GitHub Pull Request #1323

_{Note: This issue was originally created as ARROW-1821. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 1323
#1323