Make the counter persistent

[rofrano]

As a: User
I need: the hit counter to persist the last known count
So that: I don't loose track of the count after the service is restarted

Assumptions:

• We will use Redis as the persistent store
• A Redis image from Docker should be used

Tasks:

• Need to update the Vagrantfile with Redis Docker image
• Need to create a Model that uses Redis

Acceptance Criteria:

Given I have a persistent counter
When I advance the hit counter to 2
And I restart the hit counter service
And I call the hit /counter URL
Then I should see 3 returned from the service