Always run Ohai Passwd plugin to support Chef >= 14.0.13

[trinitronx]

Adds line to solo.rb config file:

 ohai.optional_plugins = [ :Passwd ] if ohai.respond_to?(:optional_plugins)

Many sprout* cookbooks use the sprout-base::home attribute, but newer versions of Chef Infra Client do not populate this Ohai attribute by default anymore!

Fix the issue by always running the Ohai :Passwd plugin to support Chef >= 14.0.13

Changes:

• Force run of Ohai Passwd plugin to populate node['etc']['passwd'] for Chef/Ohai >= 14.0.13
• Guard with ohai.respond_to?(optional_plugins) to support older Chef + Ohai versions

Build tested when merged against Pull Request #40 here. (Due to old .travis.yml RVM ruby versions that no longer worked)

References:

• https://github.com/chef/ohai/blob/master/RELEASE_NOTES.md#optional-ohai-plugins
• https://stackoverflow.com/a/57953198/64549

[trinitronx]

Note: Travis builds are broken unless .travis.yml is updated (as in #40). Build check is safe to ignore!