test: fix incorrect use of RAND_MAX

On some systems (e.g. Solaris/OpenIndiana) rand() and random() have
different ranges. RAND_MAX is the maximum value returned by rand(),
but random() should always have a range of 0 through 2^31-1.

This fixes multiple failures in different tests.

test/unit/test.c

@@ -90,7 +90,7 @@ main(int argc, char **argv)
 double
 TST_GetRandomDouble(double min, double max)
 {
-  return min + (double)random() / RAND_MAX * (max - min);
+  return min + random() / 2147483647.0 * (max - min);
 }
 
 void