Ansible 2.4 compatibility

[fullyint]

• update include to import_tasks, include_tasks or import_playbook (docs and docs).
  This avoids deprecation warning. However, server.yml will still show deprecation warning till the composer galaxy role changes these two includes.
• bump Ansible requirement to 2.4 to accommodate import_* and include_*
• add warning for Ansible versions greater than tested with Trellis
  It happens that people update Ansible but not Trellis, then run into problems, not realizing they need to update their Trellis for compatibility, posting on discourse, etc.

  [WARNING]: You Ansible version is 2.5.0.0 but this version of Trellis has only been tested for
  compatability with Ansible 2.4.0.0 -> 2.4.2.0. It is advisable to check for Trellis updates or
  downgrade your Ansible version.
  

• adjust when conditions: failed and success no longer account for rc
• move dynamic HostKeyAlgorithms from --ssh-extra-args to environment keyword
  --ssh-extra-args seemed to no longer have any effect (maybe related?)
• accommodate potential for multiple inventories (inventory list in cli.options)

  It is now possible to specify mulitple inventory sources in the command line (-i /etc/hosts1 -i /opt/hosts2) --Ansible CHANGELOG

• remove loader kwarg from VariableManager.get_vars()

[franzliedke]

Great work. 👍

A silent upgrade to Ansible 2.4 means we can not deploy our site anymore. Took us a while to find out that the Ansible upgrade was the problem.

[swalkinshaw]

Tested and working 👍

[franzliedke]

Great, thanks! Can we get a new release as well? 😇

[ztackett11]

How can I go about adding these changes to my trellis repo? i think i was able to update trellis to rc 2 (I think)