Set API Key in URL when submit distribution metrics

[tianchu]

api.Distribution.send no longer works after #446, as endpoint v1/distribution_points still expects the api key in the URL parameter than header.

To reproduce:

from datadog import initialize, api
options = {
    'api_key':'<API-KEY>',
    'app_key':'<APP-KEY>'
}
initialize(**options)

# submitting a regular metric point works
api.Metric.send(metric='my.test.metric', points=1)

# submitting a distribution metric point gets error 'No api key specified'
api.Distribution.send(distributions=[{
    'metric': 'my.dist.test',
    'points': [(1573757950, [1.0])],
    'host': None,
}])

[zippolyte]

Looks like this should solve #479. Do you confirm @tianchu

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[zippolyte]

The change looks good to me. This wasn't caught because we don't have integration tests for distributions. Would you mind adding some ?

[tianchu]

Looks like this should solve #479. Do you confirm @tianchu

Correct, it should solve $479.

[tianchu]

The change looks good to me. This wasn't caught because we don't have integration tests for distributions. Would you mind adding some ?

Makes sense. Let me look into it.

[nmuesch]

/azp run DataDog.datadogpy.integration

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[nmuesch]

Thanks for fixing this and the initial test