Fix argv parsing

Before this patch, we were using $1 both for MAX_TRACKERS and BASE_DIR, which
was insane.
Check the YAML validity of the tracker list we downloaded

This way, if we get a CloudFlare timeout instead of a legit HTTP timeout, we can
still detect something weird happened, and retry.
Use load(), as safe_load() can't handle python/unicode

Note that this is tragic and we should fix the underlying problem which is that
we generate weird python/unicode YAML structures.
Merge pull request #1410 from paulproteus/detect-more-bugimporters-api-errors

Detect more bugimporters api errors