libcontainer/intelrdt: rm init() from intelrdt.go

Use sync.Once to init Intel RDT when needed for a small speedup to
operations which do not require Intel RDT.

Simplify IntelRdtManager initialization in LinuxFactory.

Signed-off-by: Xiaochen Shen <xiaochen.shen@intel.com>

libcontainer/intelrdt/cmt.go

@@ -6,6 +6,7 @@ var (
 
 // Check if Intel RDT/CMT is enabled.
 func IsCMTEnabled() bool {
+	featuresInit()
 	return cmtEnabled
 }