Fix deadlock bug #216

Job	Run time
opentelemetry-semantic-conventions	37s
opentelemetry-getting-started	58s
opentelemetry-opentracing-shim	47s
opentelemetry-opencensus-shim	43s
opentelemetry-proto-protobuf5	32s
opentelemetry-exporter-otlp-proto-common	40s
opentelemetry-api	49s
opentelemetry-exporter-opencensus	36s
opentelemetry-sdk	50s
opentelemetry-exporter-otlp-combined	41s
opentelemetry-propagator-b3	37s
opentelemetry-exporter-zipkin-json	49s
opentelemetry-exporter-otlp-proto-grpc	43s
opentelemetry-test-utils	41s
opentelemetry-propagator-jaeger	42s
opentelemetry-exporter-otlp-proto-http	51s
opentelemetry-exporter-prometheus	42s
opentelemetry-exporter-zipkin-proto-http	38s
opentelemetry-exporter-zipkin-combined	37s
	13m 33s

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