Fix broken 'dovecot' git submodule dependencies

1) Fetch EthACKdotOrg/dovecot for via HTTPS to avoid authenticity errors
with some github.com ip addresses:

```
Cloning into 'puppet/modules/dovecot'...
The authenticity of host 'github.com (192.30.252.128)' can't be
established.
RSA key fingerprint is 16:27:ac:a5:76:28:2d:36:63:1b:56:4d:eb:df:a6:48.
Are you sure you want to continue connecting (yes/no)? ^C
fogmail (master)$ Clone of 'git@github.com:EthACKdotOrg/dovecot.git'
into submodule path 'puppet/modules/dovecot' failed
```

2) Fix referred commit for EthACKdotOrg/dovecot (previous commit was
probably squashed when feature branch was rebased for
https://github.com/mjhas/dovecot/pull/27
Merge pull request #2 from gildegoma/fix-gitsubmodules

Fix broken 'dovecot' git submodule dependencies

Thanks!

For now, I'd rather use submodules in order to avoid more dependencies.
Especially since it's not finished.
Maybe later, once modules are fixed and stabilized (especially the one for xtreemfs, being developed with now). More over, the whole stuff will be scripted, especially the "storage" part, as anyone should be able to deploy that.