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-04-aliases/content

@@ -1,3 +1,4 @@
+From: user@testserver
 Subject: Prueba desde el test
 
 Crece desde el test el futuro

test/t-04-aliases/msmtprc

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

test/t-04-aliases/run.sh

@@ -14,7 +14,7 @@ chasquid -v=2 --logfile=.logs/chasquid.log --config_dir=config &
 wait_until_ready 1025
 
 function send_and_check() {
-	run_msmtp "$1@testserver" < content
+	smtpc "$1@testserver" < content
 	shift
 	for i in "$@"; do
 		wait_for_file ".mail/$i@testserver"
@@ -42,7 +42,7 @@ send_and_check añil+blah azul índigo
 
 # Test the pipe alias separately.
 rm -f .data/pipe_alias_worked
-run_msmtp tubo@testserver < content
+smtpc tubo@testserver < content
 wait_for_file .data/pipe_alias_worked
 mail_diff content .data/pipe_alias_worked
 
@@ -58,17 +58,17 @@ send_and_check vic.uña+abc uña
 
 # Test the pipe alias separately.
 rm -f .data/pipe_alias_worked
-run_msmtp ñandú@testserver < content
+smtpc ñandú@testserver < content
 wait_for_file .data/pipe_alias_worked
 mail_diff content .data/pipe_alias_worked
 
 # Test when alias-resolve exits with an error
-if run_msmtp roto@testserver < content 2> .logs/msmtp.out; then
+if smtpc roto@testserver < content 2> .logs/smtpc.out; then
 	fail "expected delivery to roto@ to fail, but succeeded"
 fi
 
 # Test a non-existent alias.
-if run_msmtp nono@testserver < content 2> .logs/msmtp.out; then
+if smtpc nono@testserver < content 2> .logs/smtpc.out; then
 	fail "expected delivery to nono@ to fail, but succeeded"
 fi
 

test/t-04-aliases/smtpc.conf

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