rollback_code and cleanup fail unless releases_path exists on local system

[ianheggie]

if release_path doesn't exists locally, then rollback will fail since helpers.py tests for env.releases_path locally not on the remote system.

        if not env.has_key('releases'):
            if dir_exists(env.releases_path):
                env.releases = sorted(run('ls -x %(releases_path)s' % { 'releases_path':env.releases_path }).split())

My quick workaround was to change the code to (the following lines had to be moved one indent to the left as well):

        if not env.has_key('releases'):
            env.releases = sorted(run('[ -d %(releases_path)s ] && ls -x %(releases_path)s' % { 'releases_path':env.releases_path }).split())