test: Rename test directories to use an explicit order

For convenience, rename the directories so the order is explicit in the name.
Make the simple test run first, to save time if it's not working.

test/t-02-exim/config/chasquid.conf

@@ -0,0 +1,5 @@
+address: ":1025"
+monitoring_address: ":1099"
+
+mail_delivery_agent_bin: "test-mda"
+mail_delivery_agent_args: "%user%@%domain%"

test/t-02-exim/config/domains/srv-chasquid/users

@@ -0,0 +1,2 @@
+#chasquid-userdb-v1
+user SCRYPT@n:14,r:8,p:1,l:32,r00XqNmRkV505R2X6KT8+Q== aAiBBIVNNzmDXwxLLdJezFuxGtc2/wcHsy3FiOMAH4c=

test/t-02-exim/config/exim4.in

@@ -0,0 +1,62 @@
+CONFDIR = ${EXIMDIR}
+
+spool_directory = CONFDIR/spool
+exim_path = CONFDIR/exim4
+
+# No need to keep anything on the environment.
+# This is the default, but exim emits a warning if it's not set
+# (https://www.exim.org/static/doc/CVE-2016-1531.txt).
+keep_environment = 
+
+# Disable TLS for now.
+tls_advertise_hosts =
+
+# Run as the current user.
+# TODO: obviously do not hard-code it!
+exim_group = ${USER}
+exim_user = ${USER}
+
+# Listen on a non-privileged port.
+daemon_smtp_port = 2025
+
+# ACLs to let anyone send mail (for testing, obviously).
+acl_smtp_rcpt = acl_check_rcpt
+acl_smtp_data = acl_check_data
+
+begin acl
+acl_check_rcpt:
+  accept
+
+acl_check_data:
+  accept
+
+
+# Forward all incoming email to chasquid (running on :1025 in this test).
+begin routers
+
+rewritedst:
+  driver = redirect
+  data = someone@srv-chasquid
+
+forwardall:
+  driver = accept
+  transport = tochasquid
+
+begin transports
+
+tochasquid:
+  driver = smtp
+
+  # exim4 will by default detect and special-case deliveries to localhost;
+  # this avoids that behaviour and tells it to go ahead anyway.
+  allow_localhost
+  hosts_override
+
+  # chasquid will be listening on localhost:1025
+  hosts = localhost
+  port = 1025
+
+  # Add headers to help debug failures.
+  delivery_date_add
+  envelope_to_add
+  return_path_add