Correct log text for JFR perf test thresholds

[roberttoyonaga]

The JFR performance tests compare performance with JFR to an app built without JFR included at build time. The performance scoring is done like this:

(value from app with JFR - value from app without JFR) / value form app without JFR.

So the thresholds are not absolute values but are the limit on the difference in performance allowed between the with JFR and without JFR builds. I've change the logging text better reflect the intent. Please have a look when you have time. Thank you!

[jerboaa]

CI failures are:

Error:  Failures: 
Error:    PerfCheckTest.testQuarkusFullMicroProfile:538 build-and-run.log log should not contain error or warning lines that are not whitelisted. See /home/runner/work/mandrel-integration-tests/mandrel-integration-tests/ts/testsuite/target/archived-logs/org.graalvm.tests.integration.PerfCheckTest/testQuarkusFullMicroProfile/build-and-run.log and check these offending 2 lines: 
event syntax error: 'topdown-retiring/metric-id=topdown!1retiring/,TOPDOWN.SL..'
Initial error: ==> expected: <true> but was: <false>
Error:    PerfCheckTest.testQuarkusJSONParseOnce:263 build-and-run.log log should not contain error or warning lines that are not whitelisted. See /home/runner/work/mandrel-integration-tests/mandrel-integration-tests/ts/testsuite/target/archived-logs/org.graalvm.tests.integration.PerfCheckTest/testQuarkusJSONParseOnce/build-and-run.log and check these offending 2 lines: 
event syntax error: 'topdown-retiring/metric-id=topdown!1retiring/,TOPDOWN.SL..'
Initial error: ==> expected: <true> but was: <false>
Error:    PerfCheckTest.testQuarkusJSON:400 build-and-run.log log should not contain error or warning lines that are not whitelisted. See /home/runner/work/mandrel-integration-tests/mandrel-integration-tests/ts/testsuite/target/archived-logs/org.graalvm.tests.integration.PerfCheckTest/testQuarkusJSON/build-and-run.log and check these offending 2 lines: 
event syntax error: 'topdown-retiring/metric-id=topdown!1retiring/,TOPDOWN.SL..'
Initial error: ==> expected: <true> but was: <false>
[INFO] 
Error:  Tests run: 26, Failures: 3, Errors: 0, Skipped: 4

Which look like #372

[Karm]

GitHub CI does not check these, so lemme run on Jenkins pls...