Failure to start net_kernel should be handled better

[hyperthunk]

Because this error message sucks:

[systest.net] epmd: up and running on port 4369 
[systest.net] found c at port 48979
[systest.net] found b at port 56305
[systest.net] found a at port 33785
[systest.net] found systest_runner at port 49451
[systest.net] found wrangler91 at port 42944
escript: exception error: no match of right hand side value 
                 {error,
                     {shutdown,
                         {child,undefined,net_sup_dynamic,
                             {erl_distribution,start_link,
                                 [[systest_runner,shortnames]]},
                             permanent,1000,supervisor,
                             [erl_distribution]}}}
  in function  systest_runner:maybe_start_net_kernel/1 (src/systest_runner.erl, line 392)
  in call from systest_runner:execute/1 (src/systest_runner.erl, line 65)
  in call from escript:run/2 (escript.erl, line 727)
  in call from escript:start/1 (escript.erl, line 277)
  in call from init:start_it/1 
  in call from init:start_em/1 
make[1]: *** [test-profile] Error 127