RFR: 8046778 Better error messages when starting JMX agent via attach or jcmd

[Staffan Larsen]

When starting the JMX agent via jcmd, the error messages you get are very cryptic: 

$ build/macosx-x86_64-normal-server-release/jdk/bin/jcmd Sleeper ManagementAgent.start 
9979: 
java.lang.RuntimeException: Invalid option specified 

$ build/macosx-x86_64-normal-server-release/jdk/bin/jcmd Sleeper ManagementAgent.start config.file=apa 
10024: 
java.lang.RuntimeException: Config file not found 

$ build/macosx-x86_64-normal-server-release/jdk/bin/jcmd Sleeper ManagementAgent.start jmxremote.port=5000 
9979: 
sun.management.AgentConfigurationError 


This is just because errors are note propagated correctly to the jcmd. With some small changes the above can look like this: 

$ build/macosx-x86_64-normal-server-release/jdk/bin/jcmd Sleeper ManagementAgent.start 
89673: 
java.lang.RuntimeException: Invalid com.sun.management.jmxremote.port number: No port specified 

$ build/macosx-x86_64-normal-server-release/jdk/bin/jcmd Sleeper ManagementAgent.start config.file=apa 
89673: 
java.lang.RuntimeException: Config file not found: apa 

$ build/macosx-x86_64-normal-server-release/jdk/bin/jcmd Sleeper ManagementAgent.start jmxremote.port=5000 
89673: 
java.lang.RuntimeException: Password file not found: /Users/staffan/mercurial/jdk9-hs-rt/build/macosx-x86_64-normal-server-release/jdk/lib/management/jmxremote.password

webrev: http://cr.openjdk.java.net/~sla/8046778/webrev.00/
bug: https://bugs.openjdk.java.net/browse/JDK-8046778

Thanks,
/Staffan