TestPipeline.run should perhaps waitUntilFinish

https://github.com/apache/beam/blob/master/sdks/java/core/src/main/java/org/apache/beam/sdk/testing/TestPipeline.java#L124

it calls waitUntilFinish() only if
1) run wasn't called
2) enableAutoRunIfMissing is true.

However in practice both of these are false.
1) run() is, in most tests, called. So effectively if you call .run() at all, then this thing doesn't call waitUntilFinish().
2) enableAutoRunIfMissing() is set to true only via TestPipeline.enableAutoRunIfMissing(), which is called only from its own unit test.

This means that, for all tests that use TestPipeline - if the test waits until finish, it's only because of the grace of the particular runner. Which is like really bad.

We're lucky because in practice TestDataflowRunner, TestApexRunner, TestSparkRunner in run() call themselves waitUntilFinish().

However, TestFlinkRunner doesn't - i.e. there currently might be tests that actually fail in Flink runner, undetected.

The proper fix to this is to fix TestPipeline to always waitUntilFinish().
Currently testing a quick-fix in https://github.com/apache/beam/pull/2240 to make sure Flink is safe.

Imported from Jira [BEAM-1712](https://issues.apache.org/jira/browse/BEAM-1712). Original Jira may contain additional context.
Reported by: jkff.

Start with sdks/java/core/src/main/java/org/apache/beam/sdk/testing/TestPipeline.java at line 124 and inspect how run() and waitUntilFinish() interact. Compare the behavior with TestFlinkRunner and the other runners mentioned in the issue; done means TestPipeline always waits until finish after a pipeline is run, with Flink tests no longer able to complete early.

Written by the indexing model from the issue text.