chore(tests): redirect debugError to the output category of tests (#2969)

I have seen some flaky test failures where it would be nice to have run the tests with `DEBUG=puppeteer:error`. Instead of always running tests like that, I am redirecting `debugError` to the output category of the test. This is the same thing that we do for Chromium's stderr.

As a drive-by, I added an additional `debugError` where we were usually a try..finally pattern.

lib/Tracing.js

@@ -13,7 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-const {helper, assert} = require('./helper');
+const {helper, assert, debugError} = require('./helper');
 const fs = require('fs');
 
 const openAsync = helper.promisify(fs.open);
@@ -89,6 +89,8 @@ class Tracing {
     let resultBuffer = null;
     try {
       resultBuffer = Buffer.concat(bufs);
+    } catch (error) {
+      debugError(error);
     } finally {
       return resultBuffer;
     }