Added functionality to catch capistrano errors. Fixes issue 176.

@brettweavnet ... @rickmendes ... This is for issue 176 https://github.com/intuit/simple_deploy/issues/176 

This bubbles up the errors so that deployments fail to multiple stacks, but it currently fails the existing specs.  I need to dig in and find out if I am breaking other funtionality or if the specs simply need to be updated.

We can chat about it tomorrow.