Add more help messages to cloudcfg utility

- Added default blurb for help text to show the 3 kinds of requests possible
- Generate request-type specific help text (e.g., trying 'cloudcfg run' will provide usage helptext on the run command.)

```
$ ./output/go/cloudcfg
usage: cloudcfg -h <host> [-c config/file.json] [-p <hostPort>:<containerPort>,..., <hostPort-n>:<containerPort-n>] <method> <methodArgs>

  Kubernetes REST API:
  cloudcfg [OPTIONS] get|list|create|delete|update <url>

  Run an image:
  cloudcfg [OPTIONS] run <image> <replicas> <name>

  Manage replication controllers:
  cloudcfg [OPTIONS] stop|rm|rollingupdate <controller>

  Options:
  -auth="/Users/tlow/.kubernetes_auth": Path to the auth info file.  If missing, prompt the user
  -c="": Path to the config file.
  -h="": The host to connect to.
  -json=false: If true, print raw JSON for responses
  -l="": Label query to use for listing
  -p="": The port spec, comma-separated list of <external>:<internal>,...
  -s=-1: If positive, create and run a corresponding service on this port, only used with 'run'
  -u=1m0s: Update interarrival period
  -v=false: Print the version number.
  -yaml=false: If true, print raw YAML for responses

$ ./output/go/cloudcfg rollingupdate
2014/06/12 11:13:18 usage: cloudcfg [OPTIONS] stop|rm|rollingupdate <controller>
$ ./output/go/cloudcfg get
2014/06/12 11:13:22 usage: cloudcfg [OPTIONS] get|list|create|update|delete <url>
$ ./output/go/cloudcfg run
2014/06/12 11:13:25 usage: cloudcfg [OPTIONS] run <image> <replicas> <name>
```
You should be able to just pass "usage" here, right?