compare_tests: Fix usage and exit codes.
compare_jobs.sh: Handle the new return codes.

compare_test has now 5 exit codes:
0: no change
1: improvements
2: regressions
3: no logs in common, cannot compare
4: extra logs in either previous or current

Exit codes 2, 3 and 4 are reported as failures by compare_jobs.sh,
with different error messages in the report table.

Change-Id: I7313ed38cd4cbb5ab1c6795391a6977f3576562a
diff --git a/compare_jobs.sh b/compare_jobs.sh
index 3684717..61cf545 100755
--- a/compare_jobs.sh
+++ b/compare_jobs.sh
@@ -193,11 +193,11 @@
     ret=$?
     if [ ! -d "${ref}" ]; then
 	printf "\t# REF RESULTS NOT PRESENT: BUILD FAILED\n" >> ${mylog}
-	ret=3
+	ret=5
     fi
     if [ ! -d "${build}" ]; then
 	printf "\t# BUILD RESULTS NOT PRESENT: BUILD FAILED\n" >> ${mylog}
-	ret=3
+	ret=5
     fi
     case $ret in
 	0)  # No change
@@ -211,10 +211,21 @@
 	    message=FAILED
 	    failed=true
 	    ;;
-	3) # Build failed
+	3) # No common logs
+	    color=red
+	    message=NO-COMMON-LOGS
+	    failed=true
+	    ;;
+	4) # Extra logs
+	    color=red
+	    message=EXTRA-LOGS
+	    failed=true
+	    ;;
+	5) # Build failed
 	    color=darkred
 	    message=BUILDFAILED
 	    failed=true
+	    ;;
     esac
 
     ${failed} && status=1