Testing fifo things in CI

Turns out the bigtest golden ref is failing a_count_diff, need to fix that before removing the default statement.

Base example code is fine.  New shell script to run default case and then nofullskip.
Expects returncode=2 after running nofullskip.

docs/examples/fifo/fifo.sh

@@ -0,0 +1,8 @@
+#!/bin/bash
+
+python3 $SBY_MAIN -f fifo.sby && python3 $SBY_MAIN -f fifo.sby nofullskip
+
+if [[ $? -ne 2 ]] ; then
+    echo "Unexpected result"
+    exit 1
+fi