test: Unify (most) SMTP client calls

To send mails, today some tests use msmtp and others our internal smtpc.py.

This works, but msmtp slows down the tests significantly, and smtpc.py
is also not particularly fast, and also has some limitations.

This patch introduces a new SMTP client tool written in Go, and makes
almost all the tests use it.

Some tests still remain on msmtp, mainly for client-check compatibility.
It's likely that this will be moved in later patches to a separate
special-purpose test.

With this patch, integration tests take ~20% less time than before.

test/t-13-reload/config/chasquid.conf

@@ -1,5 +1,6 @@
 smtp_address: ":1025"
 submission_address: ":1587"
+submission_over_tls_address: ":1465"
 monitoring_address: ":1099"
 
 mail_delivery_agent_bin: "test-mda"

test/t-13-reload/msmtprc

@@ -1,14 +0,0 @@
-account default
-
-host testserver
-port 1587
-
-tls on
-tls_trust_file config/certs/testserver/fullchain.pem
-
-from someone@testserver
-
-auth on
-user someone@testserver
-password password222
-

test/t-13-reload/run.sh

@@ -22,7 +22,7 @@ chasquid -v=2 --logfile=.logs/chasquid.log --config_dir=config \
 wait_until_ready 1025
 
 # First, check that delivery fails with the "wrong" password.
-if run_msmtp someone@testserver < content 2>/dev/null; then
+if smtpc someone@testserver < content 2>/dev/null; then
 	fail "success using the wrong password"
 fi
 
@@ -32,7 +32,7 @@ chasquid-util-user-add someone@testserver password222
 echo "analias: someone" > config/domains/testserver/aliases
 sleep 0.2
 
-run_msmtp analias@testserver < content
+smtpc analias@testserver < content
 wait_for_file .mail/someone@testserver
 
 
@@ -50,7 +50,7 @@ sleep 0.2
 
 # Send another mail.
 rm .mail/someone@testserver
-run_msmtp analias@testserver < content
+smtpc analias@testserver < content
 wait_for_file .mail/someone@testserver
 
 # Check there are new entries.

test/t-13-reload/smtpc.conf

@@ -0,0 +1,4 @@
+addr localhost:1465
+server_cert config/certs/testserver/fullchain.pem
+user someone@testserver
+password password222