'-a' flag produces different output than '-a='

for example, when listing configs:

``` console
ENG000656:workflow aaronschlesinger$ deis config:list -a test1
=== test1 Config
A B
FOO 1
ONE 1
ENG000656:workflow aaronschlesinger$ deis config:list -a=test1
=== =test1 Config
```

The former and the latter should produce the same output, or one should error.

Replaces deis/workflow#127

Start at the config:list command and its argument or flag parsing, then reproduce both `-a test1` and `-a=test1` forms. Done means both forms produce identical output, or the command consistently rejects one form; add or update coverage if the command has existing tests.

Scritto dal modello di indicizzazione a partire dal testo della issue.