DB backups and tar gzipper to use open3 and not assume /var/vcap

* Move /var/vcap assumptions into the startup scripts in release
* Use MYSQL_PWD environment variable instead of command line option for
  mysqldump
* Prefer commandline options to output to file over shell stdout
  redirection
improve rake shipit CI check error description
Fix deployer test to check not nil
Deployer specification test refactor