Log command exit status
Some Capistrano users were confused about such messages

DEBUG [247d7a19] Command: [ -f /projects/myproject/releases/20131017094531/config/database.yml ]
DEBUG [247d7a19] Finished in 0.114 seconds command failed.

And asked me if it's fine when 'command failed'

With this change users will see the exit status of command.
Merge pull request #33 from kirs/verbose-command-result

Log command exit status