add set_tags to set batches of tags can be set in a single VOSpace call.  Modified set_tag to use set_tags so that all the prop setting commands are in one place.
bump up the default prefetch limit to 10 files...
ensure that vos connections are closed when building an hdulist.
ensure that vos connection get closed after data read.
added some logging of exceptions.
added some feedback when application is waiting for file from VOS.
Merge remote-tracking branch 'origin/master'

Conflicts:
	src/ossos-pipeline/ossos/downloads/core.py
have buff return outside try/except block to make code cleaner to understand.