Preparations for Python 3.5 D-Day.

[ludeeus]

Description:

This is a big one...

Changes:

• Various tweaks to both python and homeassistant suites.
• Added a python-migration function
  • This handles checks if migration is needed and notify the user about it.
  • It "stores" the current pyversion in a file /srv/homeassistant/hassbian/pythonmigration
  • If the install script for HA is run, the user will not get a choice (this should only be used the first time anyway)
• Added a new systeminfo function (Should be it's own PR...I know....)
  • This prints useful system information before running install/upgrade/remove scripts.
  • If there is an update to hassbian-config if will show that as well.

Related issue (if applicable): Fixes #

Checklist (Required):

• The code change is tested and works locally.
• The code is compliant with Contributing guidelines

If pertinent:

• Script has validation check of the job.
• Created/Updated documentation at /docs

[Landrash]

systeminfo is missing form "tab completion"

[Landrash]

Error on Stretch

Checking current version...
3.5.3/opt/hassbian/suites/python.sh: line 29: python3.7: command not found
Upgrading to Python 3.7.3

[Landrash]

LGTM. Tested on Stretch and Buster