Add --max-nondet-string-length option to regression test

Author: danpoe

jbmc/regression/jbmc/no-main-multi-array-maybe-null2/test.desc

@@ -1,6 +1,6 @@
 CORE
 Main.class
---function Main.main
+--function Main.main --max-nondet-string-length 10000
 ^EXIT=10$
 ^SIGNAL=0$
 ^VERIFICATION FAILED$