Extend the testing config file format so that it allows to specify whether to run the monitor script or not

[mulkieran]

Currently, there is only one key, the one that is used to specify the devices that may be used. We should add another key, say "dbus-monitor" and we should modify the parse_json.py script appropriately to add the extra "--monitor-dbus" option to the command-line args as appropriate. Some modification will have to be done to stratis-blackbox-tests.sh.