Implement initial 'wdcli backup_instance' command

This commit performs an initial implementation of the 'backup_instance'
command.

env/runtime.go

@@ -0,0 +1,13 @@
+package env
+
+import "path/filepath"
+
+// RuntimeDir returns the path to the runtime directory
+func (dis Distillery) RuntimeDir() string {
+	return filepath.Join(dis.Config.DeployRoot, "runtime")
+}
+
+// RuntimeUtilsDir returns the path to the runtime utility dir
+func (dis Distillery) RuntimeUtilsDir() string {
+	return filepath.Join(dis.Config.DeployRoot, "runtime", "utils")
+}