Adding ability to 'require' a pkg be installed on every IA run

[jbaker10]

This allows an admin to add a key in the bootstrap.json file specifying a package as "required" using a boolean true or false. Meaning that upon ever IA run, regardless of previous install status, the "required" package should always be (re)installed.

   {
      ...
      "version":"1.0",
      "required": false
    },
    {
      ...
      "version":"1.0",
      "required": true
    }

If the "required" key is not present, it will be assumed to be False, and the normal checks will ensue.