Clean up & remove commented-out ChefSpec code
Reorganize default ChefSpec, use correct assertions for tests

* Instead of `chef_run.should`, use `expect(chef_run).to`
* DRY up some tests for repetitive actions (e.g., including recipes)
Add missing specs to ChefSpec default_spec
Remove code that does nothing in ChefSpec spec_helper

Scope of these actions is incorrect; doesn't actually have any effect
Set platform & version in ChefSpec tests config
Refactor ChefSpec stubbing etc. to shared method in spec_helper
Add ChefSpec tests for et_haproxy::syslog recipe
Add ChefSpec tests for et_haproxy::newrelic recipe
Move custom matchers to ChefSpec suggested location

See
https://github.com/sethvargo/chefspec/tree/v4.0.0#writing-custom-matchers
for details
Add ChefSpec tests for stunnel, add necessary custom matchers

Opened hw-cookbooks/stunnel#20 to try & get these custom matchers
merged into the actual stunnel cookbook.