The errors testcases use -module to obtain a unique module name

Fixes parallel make where each invocation of swig was writing and
deleting the same file resulting in lots of the newly introduced
warning messages:

  On exit, could not delete file xxx.py: No such file or directory

Examples/test-suite/errors/cpp_namespace_template_bad.i

@@ -1,4 +1,4 @@
-%module namespace_template
+%module xxx
 
 namespace test {
   template<typename T> T max(T a, T b) { return (a > b) ? a : b; }