add small subcommand to validate config

client/configcheck.go

@@ -0,0 +1,8 @@
+package client
+
+import "github.com/zrepl/zrepl/config"
+
+func RunConfigcheck(conf *config.Config, args []string) error {
+	// TODO: do the 'build' steps, e.g. build the jobs and see if that fails
+	return nil
+}