Update Cookbook to use HTTPS repos

[thomasriley]

The cookbook is currently accessing the Sensu repos via HTTP by default. We should update the cookbook to use HTTPS instead.

Expected Behavior

Packages should be downloaded via HTTPS only.

Current Behavior

Packages are downloaded via HTTP

[thomasriley]

Update the repos to use HTTPS for:

• Sensu
• Sensu Enterprise

[majormoses]

We now download the pgp key over https so the risk of MITM has gone down drastically I am not sure the benefits of using https when we are already verifying integrity with gpg. I am fine with leaving this open buts certainly not a high priority anymore.