ID-925 Fix register-user integration test flakiness.

[Ghost-in-a-Jar]

https://broadworkbench.atlassian.net/browse/ID-925

The register-user ui integration test is being flakey and I think that the registration flow in orchestration that we changes recently is the cause. In a for yield, futures run concurrently and not necessarily in order unless they depend on results from eachother. So I think what is happening is that sometimes the register request to sam finishes before the rest but when it doesnt we get an error from thurloe and the test fails. By awaiting the sam registration call we make sure it finishes first.

I think this is probably affecting users in production that are trying to register, hard to say how many are actually hitting this.

It is generally good to avoid awaiting futures, but in this case i think it makes sense, register user isnt a high volume endpoint so I am not worried about the marginal performance loss. An alternative is to do future.onSuccess or something but I like the simplicity and straightforward nature of the await here.

Have you read CONTRIBUTING.md lately? If not, do that first.

I, the developer opening this PR, do solemnly pinky swear that:

• I've followed the instructions if I've made any changes to the API, especially if they're breaking changes
• I've updated the RC_XXX release ticket with any manual steps required to release this change
• I've updated the FISMA documentation if I've made any security-related changes, including auth, encryption, or auditing

In all cases:

• Get two thumbsworth of review and PO signoff if necessary
• Verify all tests go green
• Squash and merge; you can delete your branch after this unless it's for a hotfix. In that case, don't delete it!
• Test this change deployed correctly and works on dev environment after deployment

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (95ba657) 69.93% compared to head (6867b64) 69.94%.

Files	Patch %	Lines
...itute/dsde/firecloud/service/RegisterService.scala	75.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1246   +/-   ##
========================================
  Coverage    69.93%   69.94%           
========================================
  Files          101      101           
  Lines         3499     3500    +1     
  Branches       386      371   -15     
========================================
+ Hits          2447     2448    +1     
  Misses        1052     1052           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[tlangs]

Hmmm. I really don't want to Await. I know its probably not a perf concern, but its really not good practice.

Instead, can we use Future.onComplete, or something to force the completion of the Sam call before calling Thurloe?