extensions directory has incorrect ownership

[rstjohn]

Newly created NiFi clusters, installed from tar.gz, do not have permission correctly set on the extensions directory

java.io.IOException: /opt/nifi/nifi-1.9.2/./extensions directory does not have read/write privilege
        at org.apache.nifi.util.FileUtils.ensureDirectoryExistAndCanReadAndWrite(FileUtils.java:51)
        at org.apache.nifi.nar.NarAutoLoader.start(NarAutoLoader.java:56)
        at org.apache.nifi.web.server.JettyServer.start(JettyServer.java:1032)
        at org.apache.nifi.NiFi.<init>(NiFi.java:158)
        at org.apache.nifi.NiFi.<init>(NiFi.java:72)
        at org.apache.nifi.NiFi.main(NiFi.java:297)

While not causing an issue, other directories are owned by root instead on the NiFi user: bin, docs, LICENSE, NOTICE and README