RFR(M): 8204571: Add support for launching multiple startup recordings

[Markus Gronlund]

Greetings,

Please review the following change-set which aims to add support for launching multiple JFR recordings from the command-line (muiltiple -XX:StartFlightRecorder=... options)

Bug/Enh: https://bugs.openjdk.java.net/browse/JDK-8204571 
Webrev: http://cr.openjdk.java.net/~mgronlun/8204571/webrev00/ 

Thanks
Markus