Ensure that the authoritative CLI has the final say in sourced defaults

There was a bug where if multiple projects sourced an option and overrode the default, it would go to a random source. For example hub.OPT.rend.output is used by both idem and acct.

idem's default is "None" for rend.output since it has a different default for each of its subcommand. acct has a default of "yaml".

Since idem is the authoritative CLI, its default of None, should take precedence over ACCT's default override.

Manually tested -- Run "idem --config-template" with the latest version of acct and latest version of idem, verify that rend:output is "null" An integration test for this was added to idem