Added automatic system detection based on current directory.

In this patch I've added automatic system detection if the client is on the directory.
This makes things _much_ easier for the user.

In practice:
```
$ nsd sys list
Name                           Id
workshop                       521a3a73-7d5d-434d-96c5-e4732db307be
$ cd workshop
$ nsd rev list
revision             deployed who                                                     time                      description
dbc44d98136e302b5c2… true     Matteo Collina <matteo.collina@gmail.com>               2014-09-16T14:45:29.000Z  built container: fff5b38e8d3c146787d995848580faa8…
8735764f9e57b9838b1… false    Matteo Collina <matteo.collina@gmail.com>               2014-09-08T22:08:11.000Z  built container: cf28904e57b0c4b84b24d0297820e8a6…
6cd3208029943c209a5… false    Matteo Collina <matteo.collina@gmail.com>               2014-09-08T22:03:06.000Z  Updated container definition.
f398e76c26114173a18… false    Matteo Collina <matteo.collina@gmail.com>               2014-09-08T21:45:22.000Z  first commit
```

@davidmarkclements @pelger