Improve message when activation is queried before action is run

I noticed the following behavior: I invoke an action (async) and immediately I ask for the logs. I get something like this:

```
./wsk action invoke slack-channels-info
ok: invoked slack-channels-info with id cb5930907976445aaebe4a5fd661d304
ioana@Ioanas-MBP:bin [ioana-slackbot]$ ./wsk activation logs cb5930907976445aaebe4a5fd661d304
error: The requested resource does not exist. (code 353)
```

The message is misleading, there is no error, it's just that the action was not run yet (it's pending). We should fix this message.