Fix robottelo.api.client

The Python requests library has changed upstream. Make module
`robottelo.api.client` match the upstream changes.

Update the tests for this module. Use the mock library. This allows mock classes
to be dropped, manual patching/unpatching to be dropped, and function calls to
be inspected at a more granual level.
Merge pull request #1505 from Ichimonji10/fix-api-client

Fix robottelo.api.client
Update CLI activation key factory

The unlimited-content-hosts option was updated upstream. Updating the
factory to match it.

Related to #1502
Merge pull request #1504 from elyezer/fix-cli-smoke

Update CLI activation key factory
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.