Will add more tests later but this locks in all the existing warnings
and errors at least, and some of the existing non-error behavior.
Mostly I want this to exist before I actually fix#1725.
Updates #1725
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This changes the behavior of "tailscale up".
Previously "tailscale up" always did a new Start and reset all the settings.
Now "tailscale up" with no flags just brings the world [back] up.
(The opposite of "tailscale down").
But with flags, "tailscale up" now only is allowed to change
preferences if they're explicitly named in the flags. Otherwise it's
an error. Or you need to use --reset to explicitly nuke everything.
RELNOTE=tailscale up change
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Brad Fitzpatrick