[test] Make FastAMG-test deterministic

Use fixed seed instead of clock value to make results of
blocked and non-blocked version and results of different
test runs comparable.

dune/istl/paamg/test/fastamg.cc

@@ -29,7 +29,7 @@ void randomize(const M& mat, V& b)
 {
   V x=b;
 
-  srand((unsigned)std::clock());
+  srand(20030317);
 
   typedef typename V::iterator iterator;
   for(iterator i=x.begin(); i != x.end(); ++i)