Add ability to clean up multiple hosts with one rm

This one was throwing me off since you can use this style with `docker ps` etc.

ping @bfirsh 

Example:

```
$ ./bundles/1.2.0-dev/binary/docker hosts 
NAME             ACTIVE   DRIVER   STATE   URL
default                                    unix:///var/run/docker.sock
bar                       none             unix:///var/run/docker.sock
foo                       none             unix:///var/run/docker.sock
giantrobot                none             unix:///var/run/docker.sock
godzilla         *        none             unix:///var/run/docker.sock
mischiefwidget            none             unix:///var/run/docker.sock
quux                      none             unix:///var/run/docker.sock
$ ./bundles/1.2.0-dev/binary/docker hosts rm bar foo giantrobot godzilla mischiefwidget quux
$ ./bundles/1.2.0-dev/binary/docker hosts 
NAME      ACTIVE   DRIVER   STATE   URL
default   *                         unix:///var/run/docker.sock
```


Signed-off-by: Nathan LeClaire <nathan.leclaire@gmail.com>