Improve Satellite automation while discovering it

[ericzolf]

It's a bit of a catch all but I fixed/improved all this as I went through the process of creating my first Satellite using this repo, so here you are:

• ignore working and private files 'my own' in Git
• add small HOWTO on how to create a Satellite
• rename group from 'satellite' to 'satellites' (plural for groups)
• add become: true and tags sat_* to playbooks/sat_install.yml so that it's easier to select parts of it
• replace Ansible 2.8 repo through Ansible 2 so that we don't depend on latest version
• remove duplicate variables in roles/install/defaults/main.yml
• add variable satellite_force_install to the install role to be able to restart a failed installation
• multiple typos
• disabled the tuning file which is rejected by Satellite 6.8 because not valid for Postgres 9.5+
• use template instead of file+blockinfile to create the disconnected.repo
• moved the enabled repos to vars/main.yml in rhsm role so that it is easier to maintain/oversee
• extended run_sat.sh to accept SAT_ENV_FILE as environment file and be able to use ansible-playbook parameters
• small variable names corrections in sat_env.sh and more explanations

At the time of writing, I'm still waiting for the repos to finish synchronizing but it looks all good now.

[ericzolf]

I pushed two additional commits to address few more points:

• align some more names of repos for Ansible and Satellite
• add an environment variable SATELLITE_SUBS_FOR_AK to be able to configure externally the subscriptions added by default
• clarify that the howto creates a "standard" Satellite