Fix sync context Run always returns true when it ran something.

This should fix a possible edgecase where some of the scheduled items
aren't being run due to being added at the very last minute.
Change TestLazyLoad to take into account immediate results.
Rework DataCache TryGetLoading test.
Fix deadlock chance in SetUpFakeUser.
Merge pull request #302 from toggl/roosmaa-nunit-stall

Fix several bugs causing unit tests to fail occasionally. Closes #232.