Improve metadata handling of profiles

Also, improve OS profile handling

process/process_linux.go

@@ -1,9 +1,7 @@
 package process
 
-// IsKernel returns whether the process is the Kernel.
-func (p *Process) IsKernel() bool {
-	return p.Pid == 0
-}
+// SystemProcessID is the PID of the System/Kernel itself.
+const SystemProcessID = 0
 
 // specialOSInit does special OS specific Process initialization.
 func (p *Process) specialOSInit() {