949186 - Removed the curl TIMEOUT setting and replaced it with a low speed limit.

Also, added a lot of comments to the other curl settings to explain them
more thoroughly.
Fixed some comments as per mhrivnak's suggestions.
Merge branch 'rbarlow-949186'

Conflicts:
	platform/test/unit/server/test_common_download.py
	platform/test/unit/server/test_common_download_backends_curl.py