feat(yamllint): include for this repo and apply rules throughout

NOTE: Not to be merged before #183, this can be rebased after that is merged. This can be checked for suitability in the meantime.

Semi-automated using ssf-formula (v0.5.0)
Fix errors shown below:

php-formula$ $(grep "\- yamllint" .travis.yml | sed -e "s:^\s\+-\s\(.*\):\1:")
./test/integration/default/inspec.yml
  1:1       warning  missing document start "---"  (document-start)

pillar.example
  3:1       warning  missing document start "---"  (document-start)
  7:22      warning  truthy value should be one of [false, true]  (truthy)
  8:22      warning  truthy value should be one of [false, true]  (truthy)
  10:22     warning  truthy value should be one of [false, true]  (truthy)
  16:17     warning  truthy value should be one of [false, true]  (truthy)
  41:12     error    wrong indentation: expected 10 but found 11  (indentation)
  46:27     warning  truthy value should be one of [false, true]  (truthy)
  70:18     warning  truthy value should be one of [false, true]  (truthy)
  74:19     warning  truthy value should be one of [false, true]  (truthy)
  83:22     warning  truthy value should be one of [false, true]  (truthy)
  97:22     warning  truthy value should be one of [false, true]  (truthy)
  107:89    error    line too long (93 > 88 characters)  (line-length)
  118:20    warning  truthy value should be one of [false, true]  (truthy)
  126:14    error    wrong indentation: expected 12 but found 13  (indentation)
  126:23    warning  truthy value should be one of [false, true]  (truthy)
  151:20    warning  truthy value should be one of [false, true]  (truthy)
  177:19    warning  truthy value should be one of [false, true]  (truthy)
  197:25    warning  truthy value should be one of [false, true]  (truthy)

Refer back to: https://github.com/saltstack-formulas/template-formula/pull/159#issue-305203039.

saltstack-formulas / php-formula

feat(yamllint): include for this repo and apply rules throughout #192