The subtest of TestSubtestPanic is expected to fail, but that must not
make the testuite of package 'suite' to fail. So call Skip to make 'go
test' to ignore that expected failure.

We are doing dirty things with testing.InternalTest. It looks like test
names should have the same prefix as the parent test, like if they were
true subtests (testing.T.Run).

So until we drop our usage of testing.InternamTest, let's rename the
tests.

Also added a few checks of the testing.RunTests result.