Add method `EntityReadMixin.read_raw`

`read_raw` makes a call to the server being tested and returns a
`requests.models.Response` object. It does not perform any validation, such as
checking the HTTP response code or decoding JSON.

Make `EntityReadMixin.read_json` call `EntityReadMixin.read_json`.
Remove 404 handling logic from `EntityReadMixin.read_json` and add this logic to
class `ActivationKey`. The 404 handling logic is only relevant to activation
keys.

Make module `test_multiple_paths` call `read_raw` instead of directly calling
`robottelo.api.client`.
Merge pull request #1500 from Ichimonji10/read-raw

Add method `EntityReadMixin.read_raw`
Cleanup old API code

Drop the records code in favor of the new API code. Also remove tests
and documentation related to the old code.
Update PERMISSIONS constant

The permissions have changed upstream, this updates the PERMISSIONS
constant to match the new changes.

Related to #1507
Add NetmaskField and update Subnet entity

Due to recent upstream builds the mask Subnet's fields are being
validated for a valid netmask value. This adds a NetmaskField that
generates valid netmasks using FauxFactory gen_netmask generator. Also
updates the Subnet's mask field to NetmaskField.

Related to #1514
Merge pull request #1509 from elyezer/update-permissions-constant

Update PERMISSIONS constant
Merge pull request #1515 from elyezer/update-subnet-entity

Add NetmaskField and update Subnet entity
Merge pull request #1506 from elyezer/cleanup-old-api-code

Cleanup old API code
Added rough draft of the Robottelo code standards

This is the initial draft of the Robottelo Code Standards.
I have created the format and some basic guidelines and background.
However, it will be up to the other members of the team to fill in
items that they feel are important.