Fix misc. linter issues (comments, variable naming, etc.)

We've accumulated a few linter issues around comments and a couple of
variable names.

While none of them is major, this patch cleans them up so it's easier to
go through the linter output, and we can start being more strict about
it.

internal/testlib/testlib.go

@@ -137,7 +137,7 @@ func (c dumbCourier) Deliver(from string, to string, data []byte) (error, bool)
 // DumbCourier always succeeds delivery, and ignores everything.
 var DumbCourier = dumbCourier{}
 
-// generateCert generates a new, INSECURE self-signed certificate and writes
+// GenerateCert generates a new, INSECURE self-signed certificate and writes
 // it to a pair of (cert.pem, key.pem) files to the given path.
 // Note the certificate is only useful for testing purposes.
 func GenerateCert(path string) (*tls.Config, error) {