Handle error when fetching gateways

Previously this error was not handled at the top level, resulting in a
panic if the gateways could not be populated.
This patch removes the logging when fetching the JSON as this double
handles the error (it logs it and returns it to be handled again), and
handles it at the top level instead where we log it an exit (keeping the
same behavior as the panic but with a nice error message and no stack
dump).

Signed-off-by: Sam Whited <sam@samwhited.com>