[enhancement] new method to determine the latest installed date

[username-is-already-taken2]

Hi there

This came up on the #compliance slack channel. The idea is that we create a method that would allow use to write a control where we can check the number of days since the last patch was installed.
i.e.

control 'os-patch-date-1.1' do
  impact 0.5
  title 'Check OS for last patching date - windows'
  desc 'This test will check windows applied a patch in the last 90 days'
  describe patch_date do
    its('days_since_last_patch_installed') { should be <= 90 }
  end
end

I've tried having ago to writing this myself but I've hit a gap in my ruby knowledge and would appreciate a steer.

You already did the ground work to get an array of hotfixes installed. I amended that to include InstalledOn property

I now have an array with items like this

{"Status"=>nil,
  "Description"=>"Security Update",
  "HotFixId"=>"KB3135173",
  "Caption"=>"http://support.microsoft.com/?kbid=3135173",
  "InstallDate"=>nil,
  "InstalledBy"=>"NT AUTHORITY\\SYSTEM",
  "InstalledOn"=>{"value"=>"/Date(1480636800000)/", "DateTime"=>"02 December 2016 00:00:00"}},
 {"Status"=>nil,
  "Description"=>"Update",
  "HotFixId"=>"KB3139907",
  "Caption"=>"http://support.microsoft.com/?kbid=3139907",
  "InstallDate"=>nil,
  "InstalledBy"=>"NT AUTHORITY\\SYSTEM",
  "InstalledOn"=>{"value"=>"/Date(1454457600000)/", "DateTime"=>"03 February 2016 00:00:00"}},
....

So I'm trying to find the lastest InstalledOn so I'm thinking I should sort the array and take the first one?

Once I have the date I was going to parse it and return the number of days.

Let me know what you think, I did think of getting powershell to do the sort for me but where's the fun in that :)