Similar to how we bake in the DERPMap to ensure that we can reach the
DERP servers if DNS isn't working, also bake in the control key for the
default control server that we use if the control server is down.
Updates #13890
Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: I18ef0381e266bd3db10063685993bc3cb76b2f42