qga: allow configuration file path via the cli

qga: allow configuration file path via the cli

Allowing the user to set the QGA_CONF environment variable to change
the default configuration file path is very unusual practice, made
more obscure since this ability is not documented.

This introduces the more normal '-c PATH'  / '--config=PATH' command
line argument approach. This requires that we parse the comamnd line
twice, since we want the command line arguments to take priority over
the configuration file settings in general.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Konstantin Kostiuk <kkostiuk@redhat.com>
Message-ID: <20240712132459.3974109-22-berrange@redhat.com>
Signed-off-by: Konstantin Kostiuk <kkostiuk@redhat.com>