R1:5cb683257249

Fix usage of fprintf() in `bin/drydock command`

Summary: See PHI513. `fprintf()` takes `(thing, pattern, args, ...)` but we aren't passing a `pattern`, so if the command returns a "%" in the output we get an error.

Test Plan:
- Installed `bytes`, a great useful program which prints all the bytes, on my HoaxOS(tm) system (see D19102).

```
epriestley@orbital ~/dev/phabricator $ ./bin/drydock command --lease 76287 -- bytes # Before patch.
[2018-03-29 02:09:08] ERROR 2: fprintf(): Too few arguments at…