Add new username type

Parsing usernames would be a fairly common thing todo from heat
metadata, this type allows what would be expected to cover most sane
usernames.

Change-Id: I3a5577d2c5bef1ce54629a0b99e2dc085d274f02

os_apply_config/tests/test_value_type.py

@@ -143,3 +143,16 @@ class ValueTypeTestCase(testtools.TestCase):
                           value_types.ensure_type,
                           test_swiftdevices,
                           'swiftdevices')
+
+    def test_username(self):
+        for test_username in ['guest', 'guest_13-42']:
+            self.assertEqual(test_username, value_types.ensure_type(
+                             test_username,
+                             'username'))
+
+    def test_username_bad(self):
+        for test_username in ['guest`ls`', 'guest$PASSWD', 'guest 2']:
+            self.assertRaises(config_exception.ConfigException,
+                              value_types.ensure_type,
+                              test_username,
+                              'username')

os_apply_config/value_types.py

@@ -28,6 +28,7 @@ TYPES = {
            "(?#/dbname)(/[a-zA-Z0-9_-]+)?"
            "(?#?variable=value)(\?[a-zA-Z0-9=_-]+)?$",
     "swiftdevices": "^(r\d+z\d+-[A-Za-z0-9.-_]+:%PORT%/[^,]+,?)+$",
+    "username": "^[A-Za-z0-9_-]+$",
     "raw": ""
 }