Fix #3417. sql-sync dump filename not automatically generated

[weitzman]

One downside of this fix is that running this code with a prior version of Drush will cause your dump files to be names auto instead of date based backups. I think mismatched Drush versions are a lot less common now that we are local to the project.

[weitzman]

I will add that sql:sync should be working even without this fix so I'm not sure whats going on in the BLT test failure. Our sql:sync tests have been passing and they dont pass --result-file. Could you try with this one line change and see if sql:sync starts succeeding?

[greg-1-anderson]

'result-file' => true should make backend invoke use --result-file; maybe some bug is causing it to insert --result-file=1 instead?

The => NULL trick is only for unish, if I recall correctly.

[weitzman]

Could be ... But --result-file without a value is now invalid. That option requires a value. I just pushed a commit which documents this. This change went in at #3370.

[grasmash]

I can verify that this does resolve the initial issue, and causes acquia/blt tests to pass.