The latest version of the ec2-scripts package includes a completely
rewritten "use EC2 ephemeral disks for swap space" script. Now that
we have something which works on recent versions of FreeBSD, turn it
on since it's a great way to use the ephemeral disks.
Note that the option for controlling this, ec2_ephemeral_swap_enable,
is not the same as the option (ec2_ephemeralswap_enable) used with the
previous ephemeral-swap script; this change was deliberate to avoid
astonishment for users who upgraded their ec2-scripts package and had
a setting left behind in rc.conf.