Git - Make sure there is a git executable available on the system, or act accordingly

[hartym]

CRIT:0000:root: Uncaught exception (in thread 139771255863040).
│ Traceback (most recent call last):
│   File "/usr/local/bin/django-zero", line 11, in <module>
│     sys.exit(main())
│   File "/usr/local/lib/python3.5/dist-packages/django_zero/commands/__init__.py", line 57, in main
│     return handler(*rest, **options)
│   File "/usr/local/lib/python3.5/dist-packages/django_zero/commands/create.py", line 29, in handle
│     return self.handle_project(*args, **options)
│   File "/usr/local/lib/python3.5/dist-packages/django_zero/commands/create.py", line 70, in handle_project
│     from medikit.commands import handle_update
│   File "/usr/local/lib/python3.5/dist-packages/medikit/commands/__init__.py", line 2, in <module>
│     from medikit.commands.pipeline import PipelineCommand
│   File "/usr/local/lib/python3.5/dist-packages/medikit/commands/pipeline.py", line 7, in <module>
│     from medikit.commands.utils import _read_configuration
│   File "/usr/local/lib/python3.5/dist-packages/medikit/commands/utils.py", line 4, in <module>
│     from medikit.config import read_configuration
│   File "/usr/local/lib/python3.5/dist-packages/medikit/config/__init__.py", line 5, in <module>
│     from medikit.config.defaults import setup_default_pipelines
│   File "/usr/local/lib/python3.5/dist-packages/medikit/config/defaults.py", line 1, in <module>
│     from medikit import steps
│   File "/usr/local/lib/python3.5/dist-packages/medikit/steps/__init__.py", line 2, in <module>
│     from medikit.steps.install import Install
│   File "/usr/local/lib/python3.5/dist-packages/medikit/steps/install.py", line 3, in <module>
│     from medikit.steps.exec import System
│   File "/usr/local/lib/python3.5/dist-packages/medikit/steps/exec.py", line 6, in <module>
│     from git import Repo
│   File "/usr/local/lib/python3.5/dist-packages/git/__init__.py", line 82, in <module>
│     refresh()
│   File "/usr/local/lib/python3.5/dist-packages/git/__init__.py", line 73, in refresh
│     if not Git.refresh(path=path):
│   File "/usr/local/lib/python3.5/dist-packages/git/cmd.py", line 293, in refresh
│     raise ImportError(err)
└ ImportError  Bad git executable.
               The git executable must be specified in one of the following ways:
                   - be included in your $PATH
                   - be set via $GIT_PYTHON_GIT_EXECUTABLE
                   - explicitly set via git.refresh()

               All git commands will error until this is rectified.

               This initial warning can be silenced or aggravated in the future by setting the
               $GIT_PYTHON_REFRESH environment variable. Use one of the following values:
                   - quiet|q|silence|s|none|n|0: for no warning or exception
                   - warn|w|warning|1: for a printed warning
                   - error|e|raise|r|2: for a raised exception

               Example:
                   export GIT_PYTHON_REFRESH=quiet