src/conf.py: set default banmask to host.

`*!user@host` is very easy to evade as most of users don't have identd server. This makes bans a little more difficult to evade.

See also:
* weechat/weechat#18
* ProgVal/Limnoria#689
Channel: fix test.py .
fix previous commit
Merge pull request #690 from Mkaysi/patch-1

src/conf.py: set default banmask to host.