No way to avoid loading the sampling_rule.json file

Would it be possible to only load this file if the LocalSampler is initialized?

Moving

`with open(resource_filename(__name__, 'sampling_rule.json')) as f:
local_sampling_rule = json.load(f)
`
to `def __init__(self, rules=local_sampling_rule):`

_Originally posted by @christianbeland in https://github.com/aws/aws-xray-sdk-python/issues/105#issuecomment-428700941_