test: clean up system-test setup against emulator

[skuruppu]

Use Docker image instead of manually downloading the emulator binary and running it.

[olavloite]

EDIT: This seems to be caused by a race condition where the Rollback call is executed before the UPDATE ... statement has executed

The timeout in the integration tests against the emulator is caused by an eternal aborted-retry loop in ITReadWriteAutocommitSpannerTest. What happens in the following:

1. Transaction 1 sends UPDATE TEST SET NAME='test18' WHERE ID=1000 and then almost directly calls Rollback without waiting for the answer for the UPDATE ... statement.
2. Transaction 2 executes DELETE FROM TEST WHERE ID=1000. This statement returns an Aborted error. No Rollback or Commit is called, as the transaction has already been aborted.
3. Transaction 2 is retried and executes DELETE FROM TEST WHERE ID=1000 in a new transaction. This statement returns an Aborted error. No Rollback or Commit is called, as the transaction has already been aborted.
4. ... this repeats for ever ...

It seems that the above happens when the Rollback in step 1 is executed before the UPDATE ... statement has executed (fully), as adding a small delay between the two RPCs does fix the problem.

[olavloite]

That really cleans it up a lot :-)

The test failure is not really related to this change, although it could be that the latest version of the emulator is behaving slightly differently from the previous version.