Fix bug that broke BAYESTAR localizations for PyCBC events
Fix a bug that was introduced in GWCelery 0.12.1 that broke BAYESTAR localizations for PyCBC events. In 0.12.1, the BAYESTAR data handling was changed to merge together the contents of the coinc.xml and psd.xml.gz files into a single XML document so that BAYESTAR was not sensitive to the order in which the two files were passed to it. PyCBC includes the PSD data in its initial upload, and so its psd.xml.gz file is just a copy of coinc.xml. Merging the two documents together resulted in a single file with two copies of every LIGO-LW table, which broke subsequent parsing.
Fix this by adding a special case for PyCBC to download the coinc.xml only. This has the nice side effect of reducing the latency for PyCBC events because it is no longer necessary to wait for the additional GraceDB REST API calls involved in uploading and download the additional file.
Fixes #341 (closed).