ztp: check for missing mount point before processing it

ztp/siteconfig-generator/siteConfig/siteConfig.go

@@ -258,12 +258,12 @@ func (prt *Partitions) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		err = fmt.Errorf("choose an appropritate disk size. must be greater than 0")
 	}
 
-	// run a clean to ensure path is not malformed
-	defaults.MountPoint = path.Clean(defaults.MountPoint)
 	// it's a required field
 	if defaults.MountPoint == "" {
 		err = fmt.Errorf("must provide a path for mount_point. e.g /var/path")
 	}
+	// run a clean to ensure path is not malformed
+	defaults.MountPoint = path.Clean(defaults.MountPoint)
 	// ensure path is absolute
 	if !(path.IsAbs(defaults.MountPoint)) {
 		defaults.MountPoint = path.Join("/", defaults.MountPoint)