(PDK-624) Add UpdateManager class to handle making changes to module files

[rodjek]

Abstracts away the file modification logic into its own class. This will allow
easy reuse for the future pdk update as well as a simple interface for
storing the pending changes in memory rather than on disk (less cleanup
required in the event of an interrupt). The presentation/reporting of the changes
has been separated from the logic that makes the changes, so that we can easily
tweak and modify the output as this feature develops.

---

An example where my metadata.json was missing the license field.

asmodean :0: pdk/foo (git:master → origin {2} U:3 ?:2!)$ ../bin/pdk convert
pdk (INFO): This is a potentially destructive action. Please ensure that you have committed it to a version control system or have a backup before continuing.
Do you want to continue converting this module? Yes
--- metadata.json	2017-11-22 14:19:03.616567876 +1100
+++ metadata.json.pdknew	2017-11-22 14:20:21.076163844 +1100
@@ -2,6 +2,7 @@
   "name": "rodjek-test",
   "author": "rodjek",
   "summary": "",
+  "license": "Apache-2.0",
   "source": "",
   "dependencies": [
 
Do you want to continue and make these changes to your module? Yes
asmodean :0: pdk/foo (git:master → origin {2} U:3 ?:2!)$ cat metadata.json 
{
  "name": "rodjek-test",
  "author": "rodjek",
  "summary": "",
  "license": "Apache-2.0",
  "source": "",
  "dependencies": [

  ],
  "operatingsystem_support": [
    {
      "operatingsystem": "Debian",
      "operatingsystemrelease": [
        "8"
      ]
    },
    {
      "operatingsystem": "RedHat",
      "operatingsystemrelease": [
        "7.0"
      ]
    },
    {
      "operatingsystem": "Ubuntu",
      "operatingsystemrelease": [
        "16.04"
      ]
    },
    {
      "operatingsystem": "windows",
      "operatingsystemrelease": [
        "2012 R2"
      ]
    }
  ],
  "requirements": [

  ]
}

[coveralls]

Coverage increased (+0.5%) to 93.052% when pulling 5bc5de2 on rodjek:pdk-624 into 8f61011 on puppetlabs:master.

[coveralls]

Coverage increased (+0.5%) to 93.058% when pulling 2ef10f6 on rodjek:pdk-624 into 8f61011 on puppetlabs:master.