change the need to specify 'provider' for specifying archive_center with python-cmr

[briannapagan]

In reviewing recent PR's like: #518 where under tests/unit/test_collection_queries.py we are hardcoding these queries:

query = DataCollections().cloud_hosted(True).daac("OBDAAC")
assert query.params["provider"] == "OB_DAAC"
query = DataCollections().daac("ASDC").cloud_hosted(True)
assert query.params["provider"] == "LARC_CLOUD"
query = DataCollections().cloud_hosted(True).daac("ASDC")
assert query.params["provider"] == "LARC_CLOUD"

Can we not just integrate from python_cmr the ability to search by archive_center, instead of manually adding each DAAC?