mod_dash: back to 15 iterations, to be sure

More testing suggests that in some cases 20 iterations leads
to a test that takes too much time.

To be sure, lower again the number of iterations to 15.

mod_dash/client_smpl.py

@@ -49,7 +49,7 @@
 # We iterate the DASH download of a chunk for the following number of
 # times, and we possibly variate the download rate each time.
 #
-DASH_MAX_ITERATION = 20
+DASH_MAX_ITERATION = 15
 
 class DASHClientSmpl(ClientHTTP):
     """ The MPEG DASH client """