default='', type="str", action='callback', callback=optparse_listvalue_callback)
parser.add_option ('-X','--extra',dest='extras',default={},type='str',metavar="<EXTRA_ASSIGNS>",
action="callback", callback=optparse_dictvalue_callback, nargs=1,
help="set extra/testbed-dependent flags, e.g. --extra enabled=true")
# user specifies remote aggregate/sm/component
default='', type="str", action='callback', callback=optparse_listvalue_callback)
parser.add_option ('-X','--extra',dest='extras',default={},type='str',metavar="<EXTRA_ASSIGNS>",
action="callback", callback=optparse_dictvalue_callback, nargs=1,
help="set extra/testbed-dependent flags, e.g. --extra enabled=true")
# user specifies remote aggregate/sm/component