Fix test reporting

When running the tests, we were reporting the number of errors
encountered instead of the number of failed tests. For neg tests, errors
are not test failures

Author: allanrenucci

compiler/test/dotty/tools/vulpix/ParallelTesting.scala

@@ -253,6 +253,9 @@ trait ParallelTesting extends RunnerOrchestration { self =>
     /** A set of the different failures */
     def failureReasons: Set[Failure] = _failures
 
+    /** Number of failed tests */
+    def failureCount: Int = _failures.size
+
     protected def logBuildInstructions(reporter: TestReporter, testSource: TestSource, err: Int, war: Int) = {
       val errorMsg = testSource.buildInstructions(reporter.errorCount, reporter.warningCount)
       addFailureInstruction(errorMsg)
@@ -295,7 +298,7 @@ trait ParallelTesting extends RunnerOrchestration { self =>
           "[" + ("=" * (math.max(progress - 1, 0))) +
             (if (progress > 0) ">" else "") +
             (" " * (39 - progress)) +
-            s"] completed ($tCompiled/$sourceCount, $errorCount failed, ${timestamp}s)\r"
+            s"] completed ($tCompiled/$sourceCount, $failureCount failed, ${timestamp}s)\r"
         )
 
         Thread.sleep(100)
@@ -305,7 +308,7 @@ trait ParallelTesting extends RunnerOrchestration { self =>
       val timestamp = (System.currentTimeMillis - start) / 1000
       // println, otherwise no newline and cursor at start of line
       realStdout.println(
-        s"[=======================================] completed ($sourceCount/$sourceCount, $errorCount failed, ${timestamp}s)"
+        s"[=======================================] completed ($sourceCount/$sourceCount, $failureCount failed, ${timestamp}s)"
       )
     }