RFR: JDK-8082537 - jimage should print usage when started with no args

[Jim Laskey (Oracle)]

Now prints usage.

http://cr.openjdk.java.net/~jlaskey/8082537/webrev/index.html <http://cr.openjdk.java.net/~jlaskey/8082537/webrev/index.html>
https://bugs.openjdk.java.net/browse/JDK-8082537 <https://bugs.openjdk.java.net/browse/JDK-8082537>