NIFI-5175 Updated NiFi compiled on Java 1.8 to run on Java 9

[jtstorck]

The bootstrap process (RunNiFi) detects Java 9 and adds "--add-modules=java.xml.bind" to the command to start NiFi
Updated OSUtils to detect Java 9 and reflectively invoke the Process.pid() method to get the PID of the NiFi process
Added java debug variable to nifi.sh to allow debugging of the bootstrap process (RunNiFi)

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[MikeThomsen]

+1 LGTM. Checked on macOS w/ 8 and 9 and the v8 build ran on v9.