fn: size restricted tmpfs /tmp and read-only / support (#1012)

* fn: size restricted tmpfs /tmp and read-only / support

*) read-only Root Fs Support
*) removed CPUShares from docker API. This was unused.
*) docker.Prepare() refactoring
*) added docker.configureTmpFs() for size limited tmpfs on /tmp
*) tmpfs size support in routes and resource tracker
*) fix fn-test-utils to handle sparse files better in create file

* test typo fix

api/models/route_test.go

@@ -17,6 +17,7 @@ func TestRouteSimple(t *testing.T) {
 		Format:      "http",
 		Timeout:     10,
 		IdleTimeout: 10,
+		TmpFsSize:   10,
 	}
 
 	err := route1.Validate()