Use poudriere for custom mailman package

[seankelly]

The mailman package defaults to SENDMAIL=on but we need POSTFIX=on. Previously this was done by building the port with the custom option. This required mounting /usr/ports inside the jail, installing the build dependencies, and building the port.

Poudriere automates that, allowing us to use binary packages everywhere. It has the option to keep the port updated too like the rest of the binary packages. My thinking is to run poudriere on vm1 to take advantage of its increased core count.

Current options for installed version:

Options        :
	COURIER        : off
	DOCS           : off
	EXIM4          : off
	HTDIG          : off
	NAMAZU2        : off
	NLS            : on
	OPENSMTPD      : off
	POSTFIX        : on
	SENDMAIL       : off