Fix template validation error

Commit 9c72ebccd3 introduced a bug: all template strings are validated against the disc template RegEx (which, for example, is wrong if we're testing the track template).

whipper/common/common.py

@@ -22,6 +22,7 @@
 import os
 import os.path
 import math
+import re
 import subprocess
 import unicodedata
 
@@ -280,6 +281,19 @@ def getRelativePath(targetPath, collectionPath):
         return os.path.join(rel, os.path.basename(targetPath))
 
 
+def validate_template(template, kind):
+    """
+    Raise exception if disc/track template includes invalid variables
+    """
+    if kind == 'disc':
+        matches = re.findall(r'%[^A,R,S,X,d,r,x,y]', template)
+    elif kind == 'track':
+        matches = re.findall(r'%[^A,R,S,X,a,d,n,r,s,t,x,y]', template)
+    if '%' in template and matches:
+        raise ValueError(kind + ' template string contains invalid '
+                         'variable(s): {}'.format(', '.join(matches)))
+
+
 class VersionGetter(object):
     """
     I get the version of a program by looking for it in command output