sympl-mail: replace old SMTP/POP/IMAP testing functionality

test.d/tc_dovecot.rb

IMAP

• test_imap_capabilities - check capabilities for IMAP4REV1, AUTH=PLAIN, AUTH=LOGIN and STARTTLS.
• test_imap_auth_plain - login with PLAIN auth
• test_imap_auth_plain_local_user - login with PLAIN auth with a local user
• test_imap_auth_login - login with LOGIN auth
• test_imap_auth_login_crypt - login with LOGIN auth and crypt'd password
• test_imap_auth_starttls - STARTTLS session
• ❗ test_imap_auth_ssl - LOGIN auth with STARTTLS

POP3

• test_pop3_auth - direct POP3
• ❗ test_pop3_auth_crypt - crypt'd password
• test_pop3_auth_tls - "not implemented by net/pop library", probably test STARTTLS
• ❗ test_pop3_auth_ssl - crypt'd password via SSL

SMTP

• test_deliver - test delivery to mailbox
• test_deliver_local_user - test delivery to local user
• test_imap_quotas - mailbox quota via imap
• test_deliver_with_quotas - mailbox quota smtp
• test_deliver_with_sieve - sieve delivery
• test_deliver_with_sieve_for_local_users - sieve delivery for local user
• test_deliver_with_sieve_and_quota - sieve delivery for local user with quota

test.d/tc_exim4_live.rb

AUTH

• test_smtp_capabilities - on public_ip:25, check STARTTLS, AUTH PLAIN, AUTH LOGIN are not offered. on localhost:25, check AUTH PLAIN and AUTH LOGIN are not offered, enable STARTTLS, check AUTH PLAIN and AUTH LOGIN are offered
• test_smtp_auth - AUTH PLAIN/LOGIN for plaintext pass
• test_smtp_auth_local_user AUTH PLAIN/LOGIN for local user
• ❗ test_smtp_auth_crypt - AUTH plain test for regular/start_tls
• test_ratelimiting - send 3 mails, set rate limit 1000000, send one more, drop limit to 1, send 3 messages (should fail), change limit to 100, send message (should succeed), check mail spool