Revert "send a 503 response when http loading times out"

This reverts commit f725cc2a34e095765b5d6824a4bf8b3fba6b0cf1.
Revert "send a 503 response when http loading times out"

This reverts commit f725cc2a34e095765b5d6824a4bf8b3fba6b0cf1.
send a 503 response when http loading times out
Merge branch 'loader_timeut_error' into voxmedia_thumbor

Conflicts:
	thumbor/loaders/http_loader.py