Add option for reloading postfix on changes

[pecharmin]

As a system administrator I would like to apply configuration changes to postfix by reloading it.

When using the default service restart behaviour with puppet, the postfix service is restarted.
Rolling out config changes by puppet, could terminate active connections of clients and cause application tasks to fail if those have a poor connection handling.

The module's default service handling is not changed as some users might depend on restarting the service on changes.
Also in some situations a restart of postfix is required to make changes effective: http://www.postfix.org/postconf.5.html

[pecharmin]

Hi @bodgit, kindly asking for a review on this :) I would like to switch from fork to upstream for this puppet module, when the improvement proposed here is merged.

[craig]

Hi @bodgit, could you merge this PR?

[debdolph]

Any progress here, @bodgit?