server: abstract out linux capability per platform

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

server/utils_linux.go

@@ -0,0 +1,12 @@
+// +build linux
+
+package server
+
+import (
+	"github.com/opencontainers/runtime-tools/validate"
+	"github.com/syndtr/gocapability/capability"
+)
+
+func lastCapability() capability.Cap {
+	return validate.LastCap()
+}