Remove trailing slash from url before adding path

Fix a regression added in a9a8f08f15f8ff375e408a102d604cae265cc100.

We should append a '/' to county URLs before making the request
to avoid an unneeded redirect, but we should also remove that
trailing slash before appending additional path elements that
begin with a slash.

Update the tests to make sure the URls of subjurisdictions
match the expected pattern.