Add os_family default for gitpython on RedHat

salt.gitfs.gitpython.install_from_source == False on RedHat
Not sure about other O/S'es as to what default value should be

salt/map.jinja

       }, grain='os'),
       'python_git': 'GitPython',
       'gitfs': {
+        'gitpython': {
+          'install_from_source': False,
+        },
         'pygit2': {
           'install_from_source': False,
           'git': {