Add tests for traces in one-loop checker

1: working test for the standard trace.
2: failing test for the beautified shortest trace.

Author: petr-bauch

regression/cbmc-incr-oneloop/alarm2/fancy_trace_test.desc

@@ -0,0 +1,12 @@
+KNOWNBUG
+main.c
+--incremental-loop main.0 --unwind-min 5 --unwind-max 10 --trace --beautify --no-sat-preprocessor --stop-on-fail
+^EXIT=10$
+^SIGNAL=0$
+^VERIFICATION FAILED$
+--
+^warning: ignoring
+--
+This will fail the invariant on `build_goto_trace.cpp:320` asserting certain
+properties of the last trace step. It is possible this combination of options is
+incompatible.

regression/cbmc-incr-oneloop/alarm2/trace_test.desc

@@ -0,0 +1,9 @@
+CORE
+main.c
+--incremental-loop main.0 --unwind-min 5 --unwind-max 10 --trace
+^EXIT=10$
+^SIGNAL=0$
+^VERIFICATION FAILED$
+^State \d+ file main.c function havocIO line 501 thread \d+$
+--
+^warning: ignoring