Prepare 7.21.0 snapshot #1067

Job	Run time
Build Java Client JDK8 (samples/client/echo_api/java/resttemplate)	1m 23s
Build Java Client JDK8 (samples/client/echo_api/java/okhttp-gson)	1m 11s
Build Java Client JDK8 (samples/client/echo_api/java/resteasy)	55s
Build Java Client JDK8 (samples/client/echo_api/java/apache-httpclient)	1m 21s
Build Java Client JDK8 (samples/client/echo_api/java/feign-gson)	59s
	5m 49s

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