add username's option

tiramisu/option.py

@@ -1079,6 +1079,18 @@ class URLOption(DomainnameOption):
             raise ValueError(_('invalid url, should ends with filename'))
 
 
+class UsernameOption(Option):
+    __slots__ = tuple()
+    _opt_type = 'username'
+    #regexp build with 'man 8 adduser' informations
+    username_re = re.compile(r"^[a-z_][a-z0-9_-]{0,30}[$a-z0-9_-]{0,1}$")
+
+    def _validate(self, value):
+        match = self.username_re.search(value)
+        if not match:
+            raise ValueError(_('invalid username'))
+
+
 class FilenameOption(Option):
     __slots__ = tuple()
     _opt_type = 'file'