Add onlyif attribute to zendserver::zsmanage

[evsheffield]

Since the zsmanage resource executes commands that can fail on subsequent applys (e.g. adding a vhost), it's useful to have the onlyif attribute as a way of maintaining idempotence.

[davidl-zend]

@evsheffield Thanks for you PR. I understand you rightly removed the trailing whitespace and added "," to comply with puppet styling guidelines. What does the "$onlyif" gain?

[evsheffield]

Hi @davidl-zend. Based on my understanding of the zsmanage resource, it seems that it does not guarantee idempotency implicitly as it is basically just a wrapper for exec. This is fine for many commands, but some such as vhost-add will fail on subsequent applications (e.g. because the vhost already exists). In order to prevent this failure, I thought it would be helpful to be able to specify an onlyif to prevent it from being applied if it would result in an error. Although not a part of this PR, support for unless could also be added, although the two accomplish the same goal. For example, I would like to test that the vhost I'm trying to add does not already exist, and prevent the command from happening if it does.

zendserver::zsmanage {'add vhost':
  command => 'vhost-add',
  zskey => $::zend_api_key_name,
  zssecret => $::zend_api_key_hash,
  additional_options => "-n ${app_name} -p 80 -t '${vhost_template}'",
  onlyif => '/usr/bin/test ! -f /usr/local/zend/etc/sites.d/vhost_http_mysite.com_80.conf',
}

[davidl-zend]

So as I understand the $onlyif allows you to specify your own tests.

[evsheffield]

@davidl-zend Thanks for the merge! Yes, that's correct. It basically just passes the value you specify directly through to exec's onlyif attribute.