Flynn host cli

This helps a lot when debugging crashed jobs by providing some low level tools:

```
$ flynn-host ps
JOB ID                                            STATE    STARTED         CONTROLLER APP  CONTROLLER TYPE
2b9fa1cfd0bb44c2bd428754d2a739f1                  running  12 seconds ago  example         web
420a7ac0d0d049bd96d2825576244413                  running  12 seconds ago  example         web
cd40ab6f49764b7d8e79f558e538a822                  running  13 seconds ago  example         web
ca48a15329044371990d96f411fa69dd                  running  38 seconds ago  gitreceive      app
eb1458f77b064c76b5bf790e3db195bb                  running  40 seconds ago  router          app
4e42dcd822d64deb8ea16c8d15c311e3                  running  40 seconds ago  blobstore       web
6c169451ae2049239ab523b3a19ac46d                  running  41 seconds ago  controller      scheduler
0cdf2aee94ac43df82cb272b81d9b62c                  running  42 seconds ago  controller      web
ebc7f0aecf5d4ffdba27358bd7aa0cc6                  running  47 seconds ago  postgres        web
490c9487b631445c8f135f15d2a42320                  running  47 seconds ago  postgres        postgres
flynn-discoverd-71bcf12924fe435ea04b4c90ee741e58  running  48 seconds ago                  
flynn-etcd-8ad5fdb782c64891804ad78d0a059c5b       running  48 seconds ago                  

$ flynn-host log eb1458f77b064c76b5bf790e3db195bb
[martini] Started GET /
[martini] Completed 404 Not Found in 181.885us
[martini] Started POST /routes
[martini] Completed 200 OK in 2.029744ms
[martini] Started POST /routes
[martini] Completed 200 OK in 2.065783ms
[martini] Started POST /routes
[martini] Completed 200 OK in 1.685913ms

$ flynn-host stop f434a0c519e349fc901435be03801060
f434a0c519e349fc901435be03801060 stopped

$ flynn-host ps -a
JOB ID                                            STATE    STARTED             CONTROLLER APP  CONTROLLER TYPE
cab37481fac24599970c67496ed64874                  running  9 seconds ago       example         web
2b9fa1cfd0bb44c2bd428754d2a739f1                  running  About a minute ago  example         web
420a7ac0d0d049bd96d2825576244413                  running  About a minute ago  example         web
cd40ab6f49764b7d8e79f558e538a822                  crashed  About a minute ago  example         web
ca48a15329044371990d96f411fa69dd                  running  About a minute ago  gitreceive      app
eb1458f77b064c76b5bf790e3db195bb                  running  About a minute ago  router          app
4e42dcd822d64deb8ea16c8d15c311e3                  running  About a minute ago  blobstore       web
6c169451ae2049239ab523b3a19ac46d                  running  About a minute ago  controller      scheduler
0cdf2aee94ac43df82cb272b81d9b62c                  running  About a minute ago  controller      web
ebc7f0aecf5d4ffdba27358bd7aa0cc6                  running  About a minute ago  postgres        web
490c9487b631445c8f135f15d2a42320                  running  About a minute ago  postgres        postgres
flynn-discoverd-71bcf12924fe435ea04b4c90ee741e58  running  About a minute ago                  
flynn-etcd-8ad5fdb782c64891804ad78d0a059c5b       running  About a minute ago                  

```