We wrap direct dateutil calls to handle two distinct cases:
* `common.dateutil.parse()`: We want to handle arbitrary timestamps including tz info,
then convert them to UTC.
This is used in HLS parsing, and for command line input for backfiller
* `common.dateutil.parse_utc_only()`: We want to only handle UTC timestamps,
but datetime.strptime isn't flexible enough (eg. can't handle missing fractional component).
This is used for restreamer request params.
Backdoor allows the operator to telnet into the given port, and get a python shell
running inside the process, from which you can debug, modify state (eg. set the log level),
or whatever. This is extremely useful for debugging weird states that you encounter randomly
but can't easily reproduce, without restarting the process and needing to wait until it happens again.
I ran `pyflakes` on the repo and found these bugs:
```
./common/common.py:289: undefined name 'random'
./downloader/downloader/main.py:7: 'random' imported but unused
./backfiller/backfiller/main.py:150: undefined name 'variant'
./backfiller/backfiller/main.py:158: undefined name 'timedelta'
./backfiller/backfiller/main.py:171: undefined name 'sort'
./backfiller/backfiller/main.py:173: undefined name 'sort'
```
(ok, the "imported but unused" one isn't a bug, but the rest are)
This fixes those, as well as a further issue I saw with sorting of hours.
Iterables are not sortable. As an obvious example, what if your iterable was infinite?
As a result, any attempt to sort an iterable that is not already a friendly type like a list
or tuple will result in an error. We avoid this by coercing to list, fully realising the iterable
and putting it into a form that python will let us sort. It also avoids the nasty side-effect
of mutating the list that gets passed into us, which the caller may not expect. Consider this example:
```
>>> my_hours = ["one", "two", "three"]
>>> print my_hours
["one", "two", "three"]
>>> backfill_node(base_dir, node, stream, variants, hours=my_hours, order='forward')
>>> print my_hours
["one", "three", "two"]
```
Also, one of the linter errors was non-trivial to fix - we were trying to get a list of hours
(which is an api call for a particular variant), but at a time when we weren't dealing with a single
variant. My solution was to get a list of hours for ALL variants, and take the union.