'parses the string based desired_capabilities which should be in the form
key1:val1,key2:val2'

def _parse_capabilities_string(self, capabilities_string):

    desired_capabilities = {}
    if (not capabilities_string):
        return desired_capabilities
    for cap in capabilities_string.split(','):
        (key, value) = cap.split(':', 1)
        desired_capabilities[key.strip()] = value.strip()
    return desired_capabilities
