mail.{{ domain }} confusion -> breaks mail_virtual_domains loops

[taoeffect]

So mail_virtual_domains is often looped through in configuration files. In some places mail. is prepended and in some places it's not. For example, the recent PR #35 loops through this variable in openssl.cnf:

https://github.com/taoeffect/empress/pull/35/files#diff-fc4a7a00381d9bd47edfe77044dbca15R43

The user should be the one specifying what their mail server is called, and this should not be mutated by the scripts.

This screen illustrates the problem as well:

[taoeffect]

A complete listing of all usages:

[taoeffect]

So one thing that's clearly broken is @PiPeep's PR #35 openssl.cnf: https://github.com/taoeffect/empress/pull/35/files#diff-fc4a7a00381d9bd47edfe77044dbca15R43

Which should contain the mail. prefix, or using the wildcard, or ignore it (but be explicit about that in a comment or something).

[taoeffect]

OK, @PiPeep switched to wildcards, and I think the rest of the usages of mail.{{ ... seem fine. The OpenDKIM stuff seems fine too. Apparently sent emails are signed as from default.EXAMPLE.com instead of mail.EXAMPLE.com... but our tests show that's OK.