Use `LogRecord.getMessage` to get OTLP body #394

Job	Run time
opentelemetry-api	41s
opentelemetry-exporter-opencensus	41s
opentelemetry-exporter-otlp-combined	46s
opentelemetry-exporter-otlp-proto-common	46s
opentelemetry-exporter-otlp-proto-grpc	52s
opentelemetry-exporter-otlp-proto-http	50s
opentelemetry-exporter-prometheus	36s
opentelemetry-exporter-zipkin-combined	40s
opentelemetry-exporter-zipkin-json	42s
opentelemetry-exporter-zipkin-proto-http	50s
opentelemetry-getting-started	1m 11s
opentelemetry-opencensus-shim	41s
opentelemetry-opentracing-shim	44s
opentelemetry-propagator-b3	41s
opentelemetry-propagator-jaeger	39s
opentelemetry-proto	29s
opentelemetry-semantic-conventions	33s
opentelemetry-test-utils	40s
opentelemetry-sdk	50s
	13m 52s

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