New upgrade script for Python.

[ludeeus]

Description:

This script will upgrade Python to the latest stable version.
It will also create a new virtual environment to be used for Home Assistant.
If it fails, it will revert back to the original virtual environment.

Checklist:

• The code change is tested and works locally.
  • Hassbian 1.4.0 "Stretch" (From Python 3.5.3)
  • Hassbian 1.23 "Jessie" (From Python 3.4.2)

Both tested with current dev branch of hassbian-scripts

• Script has validation check of the job.

If pertinent:

• Created/Updated documentation at /docs

[stickler-ci]

Use 'cd ... || exit' or 'cd ... || return' in case cd fails.

[stickler-ci]

Use 'cd ... || exit' or 'cd ... || return' in case cd fails.

[stickler-ci]

Double quote to prevent globbing and word splitting.

[ludeeus]

I'm unsure about this, it can help many users with the upgrade, but it's also a big change.
Maybe add this to the script?
Requiring users to take another step.

if [ "$FORCE" == "" ]; then
    echo "This script will change a lot on your pi."
    echo "DO NOT run this if you absolutely have to."
    echo "You can force run the upgrade script like this:"
    echo "sudo hassbian-config upgrade python --force"
   return 0
  fi

[Landrash]

I'm unsure about this script. What's your reason for wanting it in?

[Landrash]

Some minor cosmetic tweaks and discussion about why this should be added should probably be had.

[Landrash]

Spelling of long.

[Landrash]

Change RPI 3 to Rapsberry Pi 3.

[Landrash]

Add information that this is not recommended.

[ludeeus]

Better now? :)

[ludeeus]

The main reason is to supply an easy way of upgrading the venv that Home Assistant runs in to a least be supported on jessie (older Hassbian devices), but this will install the latest stable version of Python to comply with future compability issues, and give the benefits that Python 3.6.x have over 3.5.x.

@Landrash Since both you and I is unsure about including this, I suggest we closed it for now and revisit it later if we want :)

[Landrash]

I'm actually for this but it would be nice if you make this not run without the --force command and make it print out a warning if you try to install it anyway.