Sync skywalking upstream version and reduce Cassandra storage size #50

Job	Run time
test_docker (receiver-zipkin-activemq)	5m 6s
test	13m 22s
test_docker (receiver-zipkin-http)	7m 36s
test_docker (receiver-zipkin-kafka)	5m 26s
test_docker (receiver-zipkin-rabbitmq)	7m 30s
test_docker (receiver-zipkin-scribe)	8m 20s
test_docker (receiver-zipkin-grpc)	7m 11s
test_docker (storage-cassandra)	10m 33s
	1h 5m 4s

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