Changing primary plugin on Fedora to keyfile

[Dusty Mabe <dusty dustymabe com>]

Hey NM team/community,

I would like to propose that we switch the order of the plugins on Fedora
(next major release is Fedora 33) to be `plugins=keyfile,ifcfg-rh` so that
both keyfiles and ifcfg are still supported, but now we default to writing
out/generating keyfiles when using NM tools. If we are ever going to get away
from the ifcfg format this is a small step in the right direction.

Of course there are things to take into consideration, like existing systems.
I propose that we only have this change take effect on new installs. On existing
systems (upgrades) we leave the order of the plugins unchanged. Over time more
users will eventually opt for a new install over an upgrade so we'll have less
users to ultimately "convert" once it comes time (distant future) to actually
get rid of the ifcfg plugin.

What do you think?
Dusty