[sos] Support running inside Toolbx containers

Toolbx [1] containers are Podman containers that are designed to be
used as interactive command line environments for development and
troubleshooting the host operating system.  Currently, those trying to
use them for troubleshooting with 'sos report' have been setting the
HOST environment variable inside their containers.

It will improve the troubleshooting experience if sos(1) could detect
that it's running inside a Toolbx container and automatically configure
itself to do the right thing.

Toolbx containers can be distinguished from other Podman containers by
the presence of the /run/.toolboxenv file.

[1] https://containertoolbx.org/
    https://github.com/containers/toolbox

Resolves: #3370

Signed-off-by: Debarshi Ray <debarshir@gnome.org>

sos/__init__.py

@@ -51,6 +51,9 @@ class SoS():
     """
 
     def __init__(self, args):
+        if not os.getenv('HOST', None) and os.path.isfile('/run/.toolboxenv'):
+            os.environ['HOST'] = '/run/host'
+
         self.cmdline = args
         # define the local subcommands that exist on the system
         # first import the necessary module, then add an entry to the dict that