repseq_vdj.py: IgReC replaces spaces with underscores

Doing the opposite is not really satisfactory but, on the other hand, in such a case
we know the read name should contain spaces (because of the should-vdj format).
9 jobs for feature-a/igrec_underscore_in_read_name in 36 minutes and 14 seconds (queued for 1 second)