Re-enable test_webapp_find_change

This makes the tenant name required in the URL, which I believe is desired
for now, but maybe there will be an all-tenant view or a default tenant
in the future.

Note that the setUp method for this test suite actually had a bug that
was only approving change A twice, rather than approving B.

Change-Id: I25bd11088719e8b3465563863123d93eff16030e
Story: 2000773
Task: 3433
2 files changed