fix(modify_table_speculative_retry): Set to reasonable numbers

The modify_table nemesis which picks one of the table properties
and alter them can choose a very low percentile or value for the
speculative_retry which can cause high load of retries that may
fail the stress eventually.

sdcm/nemesis.py

@@ -2661,8 +2661,8 @@ def modify_table_speculative_retry(self):
             default: speculative_retry = '99.0PERCENTILE';
         """
         options = ("'ALWAYS'",
-                   "'%spercentile'" % random.randint(1, 99),
-                   "'%sms'" % random.randint(1, 1000))
+                   "'%spercentile'" % random.randint(95, 99),
+                   "'%sms'" % random.randint(300, 1000))
         self._modify_table_property(name="speculative_retry", val=random.choice(options))
 
     def modify_table_twcs_window_size(self):