Show open setup issue keys in "title" attribute of setup issues warning

Summary:
Ref T7184. I managed to write a phantom setup issue which fails normally and succeeds when looked at carefully, so clicking "you have open issues..." always cleared them. This made it very difficult to figure out what the problem was.

Show issue keys in the "title" attribute to make this sort of thing easier to deal with.

Test Plan: Moused over "You have issues..." text, saw issue key, quickly fixed issue with new information.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7184

Differential Revision: https://secure.phabricator.com/D11743