Make runner ignore entropy warnings.

In FIPS mode we may print a message when we're waiting for additional
entropy. These warnings should not cause runner tests to fail.

Change-Id: I2beff64344fd2fce444576181f4234c4231de444
Reviewed-on: https://boringssl-review.googlesource.com/15266
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

ssl/test/runner/runner.go

@@ -1106,7 +1106,10 @@ func runTest(test *testCase, shimPath string, mallocNumToFail int64) error {
 	}
 
 	if len(extraStderr) > 0 || (!failed && len(stderr) > 0) {
-		return fmt.Errorf("unexpected error output:\n%s\n%s", stderr, extraStderr)
+		lines := strings.Split(stderr, "\n")
+		if len(lines) != 2 || lines[1] != "" || !strings.Contains(lines[0], "The kernel entropy pool contains too few bits") {
+			return fmt.Errorf("unexpected error output:\n%s\n%s", stderr, extraStderr)
+		}
 	}
 
 	if *useValgrind && isValgrindError {