Fix race condition in logOut.

[chr15m]

This fixes a race condition where the session is saved but then modified again in the keepSessionInfo branch and the callback is called before save is called again. This patch issues a second save in the keepSessionInfo eliminating the race condition. Fixes #1004.

Checklist

• I have read the CONTRIBUTING guidelines.
• The automated test suite ($ make test) executes successfully.

I have left the following unchecked with an explanation:

• The automated code linting ($ make lint) executes successfully.

When I ran make lint I encountered an error because jshint is expected on the path (as opposed to being installed by npm and being called with npx for example). When I added it to the path it threw several errors but none of them were related to this patch. These errors are all from the existing codebase. Maybe I have run this in error somehow or I'm missing a config file.

• I have added test cases which verify the correct operation of this feature or patch.

I can't see how to replicate the failing condition in the current tests. I'm looking at request.test.js and I'm unsure how to simulate a backend which takes a while to set the values. Any guidance here welcome.

• I have added documentation pertaining to this feature or patch.

I do not think any documentation changes will be necessary for this under-the-hood fix which will be transparent to the user.