Get the process' running GID in addition to UID

[patcable]

On machines where the Java process' primary GID may not match the running GID it's possible to run into issues - specifically:

Exception in thread "main" java.io.IOException: well-known file /tmp/.java_pid22933 is not secure: file's group should be the current group (which is 9999) but the group is 999
	at sun.tools.attach.LinuxVirtualMachine.checkPermissions(Native Method)
	at sun.tools.attach.LinuxVirtualMachine.<init>(LinuxVirtualMachine.java:117)
	at sun.tools.attach.LinuxAttachProvider.attachVirtualMachine(LinuxAttachProvider.java:63)
	at com.sun.tools.attach.VirtualMachine.attach(VirtualMachine.java:208)
	at net.virtualvoid.perf.AttachOnce.loadAgent(AttachOnce.java:38)
	at net.virtualvoid.perf.AttachOnce.main(AttachOnce.java:34)

Reading the process' running group and using that as a sudo parameter avoids that error. May want to test on a system that doesn't output names (happy to do this - just need a pointer).

[brendangregg]

ok, thanks!