KNOWNBUG test for engine heuristic

This replicates issue #921.

Author: kroening

regression/ebmc/k-induction/k-induction6.desc

@@ -0,0 +1,9 @@
+KNOWNBUG
+k-induction6.sv
+
+^EXIT=10$
+^SIGNAL=0$
+--
+^warning: ignoring
+--
+The property should hold, but is reported as refuted.

regression/ebmc/k-induction/k-induction6.sv

@@ -0,0 +1,7 @@
+module main(input clk, input x);
+
+  a0: assume property (not s_eventually !x);
+
+  p0: assert property (x);
+
+endmodule