in integration test, don't read database index files but use imap idle to get notified of message delivery, and make integration & quickstart tests faster by making first-time sender delay configurable, and using a 1s timeout instead of the default 15s

we could make more types of delays configurable. the current approach isn't
great, as it results in an a default value of "0s" in the config file, while
the actual default is 15s (which is documented just above, but still).

testdata/integration/config/mox.conf

@@ -15,9 +15,13 @@ Listeners:
 		SMTP:
 			Enabled: true
 			NoSTARTTLS: true
+			FirstTimeSenderDelay: 1s
 		Submission:
 			Enabled: true
 			NoRequireSTARTTLS: true
+		IMAP:
+			Enabled: true
+			NoRequireSTARTTLS: true
 	mox2:
 		IPs:
 			- 172.28.2.10
@@ -59,6 +63,7 @@ Listeners:
 					KeyFile: ../tls/moxmail3-key.pem
 		SMTP:
 			Enabled: true
+			FirstTimeSenderDelay: 1s
 		Submission:
 			Enabled: true
 			NoRequireSTARTTLS: true