megasky dag node has BayesWave node as parent when `--separate-post-dag` is used
Could perhaps modify parent-child links to have the megasky node not have the BayesWave node as parent like here (https://git.ligo.org/lscsoft/bayeswave/blob/master/BayesWaveUtils/scripts/bayeswave_pipe#L1189). @james-clark I could this myself if it's okay with you.