Move cert change notification into ensureCertificate()

When ensureCertificate renews the cert, the filename will match the
nginx config cert file. The current code detects that this implies
that the cert has not changed and thus does not update mail container.

Move the notification into ensureCertificate() itself. If we have a wildcard
cert and it gets renewed when installing a new app, then mail container will
still get it.

src/mail.js

@@ -25,6 +25,7 @@ exports = module.exports = {
 
     startMail: restartMail,
     restartMail: restartMail,
+    handleCertChanged: handleCertChanged,
 
     sendTestMail: sendTestMail,
 
@@ -690,6 +691,10 @@ function restartMailIfActivated(callback) {
     });
 }
 
+function handleCertChanged(callback) {
+    restartMailIfActivated(callback);
+}
+
 function getDomain(domain, callback) {
     assert.strictEqual(typeof domain, 'string');
     assert.strictEqual(typeof callback, 'function');