assertProblems(foo) with an implicit empty list can be confusing to
read. You can tell I figured this out, because
GerritPublicKeyCheckerTest, which postdates the other tests, already
used this pattern. Use it consistently everywhere.
Use (String, String...) in method signatures to make invalid use of
assertProblems with no expected problems a compile-time error.
Change-Id: I5621c586ac16dff2a34d30efd1cca8949907316d
a278b95161