Added support for submitting jobs to the Open Science Grid

This PR updates bilby_pipe to support running on the Open Science Grid. The highlights are

• the bilby_pipe command-line script now supports the --osg option
• updated options for vanilla-universe checkpointing (cc @james-clark)

To support the above, I chose to do a bit of restructuring in the relevant methods to clean up how the submit files are generated, including

• moved out/err/log file path options to a method
• moved checkpointing options to a method
• moved file transfer options to a method and fixed directory names for transfer_output_files
• track extra_lines as a list, not a monolithic str (this is natively supported by pycondor anyway)
• support appending requirements to self.requirements (required for OSG options)

Fixes #103 (closed).

bilby_pipe/main.py

@@ -881,6 +881,8 @@ class Dag(object):
                 [str(self.inputs.ini)] + files,
                 [self._relative_topdir(self.inputs.outdir, self.initialdir)],
             ))
+            # condor transfers all files into a flat structure
+            files = list(map(os.path.basename, files))
 
         if self.inputs.osg:
             _osg_lines, _osg_reqs = self._osg_submit_options(