Booleans are not-mutable so you can just set the default value here so callers don't need to go digging in code to find out what it is.  i.e.

    def __init__(self, subtest, subcmd, subargs=None, timeout=None, verbose=False):

Also from a documentation perspective, parameters are documented automatically, but code is not.  Making it part of the definition means fewer manual doc. updates :D