Prepend "$app-$version-$distroshortname-" to logfile names

[christophprokop]

butido build --help
[...]
-L, --write-log
With this flag set, butido does not only write the build logs to database, but also to
the configured
log directory.

        The log of a build is written to `<log_dir>/<build id>.log`.
      [...]

---

logs are currently named $UUID.log
would be helpful to name them $UUID-$app-$version-$distroshortname.log

[primeos-work]

We decided to prepend the package name and version to the logfile name instead of appending for the reasons explained in #97.