(#2848) Migrate dns-alt-names back to settings.

Now that all the other changes have been made, the dns-alt-names can migrate
back to the settings where they apply only for generating the CSR for the
local machine.

The one exception to that rule is the puppet cert generate application, in
which we want to pass any *command line* value of dns-alt-names into the CSR
for a foreign node, but not the value from anywhere but the command line.

Since the settings now track the CLI origin of a setting, we can use that to
derive the data and pass it around appropriately to make that so.

Signed-off-by: Daniel Pittman <daniel@puppetlabs.com>