Made some work to repair checking the result of the job

I found some bugs:
1) If you do "Generate and deploy" and if there are some errors in
generate stage, plugin doesn't show any errors, just deploys and sais
that everything is OK.
2) If you do "Deploy" or "Generate and Deploy" and there are some
errors in deploying stage (for example no internet connection), plugin
still shows "octopress exec end." and no errors. This is because it
search for the "## Github Pages deploy complete", but this string
appears even if there are some problems in deploying. For example:
```
## Commiting: Site updated at 2013-03-07 14:14:10 UTC

[master b20343e] Site updated at 2013-03-07 14:14:10 UTC
 12 files changed, 247 insertions(+), 160 deletions(-)

## Pushing generated _deploy website

ssh: Could not resolve hostname github.com: nodename nor servname
provided, or not known

fatal: The remote end hung up unexpectedly

cd -

## Github Pages deploy complete
```
So I figured out with two this bugs.