Add vendoring to containerd master

Initial vendor list validated with empty $GOPATH
and only master checked out; followed by `make`
and verified that all binaries build properly.
Updates require github.com/LK4D4/vndr tool.

Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com>

vendor/github.com/docker/go-metrics/docs.go

@@ -0,0 +1,3 @@
+// This package is small wrapper around the prometheus go client to help enforce convention and best practices for metrics collection in Docker projects.
+
+package metrics