Add prometheus container level metrics

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

vendor/github.com/crosbymichael/cgroups/errors.go

@@ -0,0 +1,31 @@
+package cgroups
+
+import (
+	"errors"
+	"os"
+)
+
+var (
+	ErrInvalidPid               = errors.New("cgroups: pid must be greater than 0")
+	ErrMountPointNotExist       = errors.New("cgroups: cgroup mountpoint does not exist")
+	ErrInvalidFormat            = errors.New("cgroups: parsing file with invalid format failed")
+	ErrFreezerNotSupported      = errors.New("cgroups: freezer cgroup not supported on this system")
+	ErrMemoryNotSupported       = errors.New("cgroups: memory cgroup not supported on this system")
+	ErrCgroupDeleted            = errors.New("cgroups: cgroup deleted")
+	ErrNoCgroupMountDestination = errors.New("cgroups: cannot found cgroup mount destination")
+)
+
+// ErrorHandler is a function that handles and acts on errors
+type ErrorHandler func(err error) error
+
+// IgnoreNotExist ignores any errors that are for not existing files
+func IgnoreNotExist(err error) error {
+	if os.IsNotExist(err) {
+		return nil
+	}
+	return err
+}
+
+func errPassthrough(err error) error {
+	return err
+}