RFR(XS): JDK-8055765: Misplaced @key stress prevents MallocSiteHashOverflow.java and MallocStressTest.java tests from running

[George Triantafillou]

Please review this test fix for 8055765.  The first token of both tests 
was changed to "@test" to enable the tests to be explicitly run using 
the jtreg "-ignore:run" flag.  Since both tests can timeout during 
normal testing, they still contain the "@ignore" tag, which prevents 
them from running unless explicitly override using the jtreg 
"-ignore:run" flag.

Webrev: http://cr.openjdk.java.net/~gtriantafill/8055765/webrev/ 
<http://cr.openjdk.java.net/%7Egtriantafill/8055765/webrev/>
Bug: https://bugs.openjdk.java.net/browse/JDK-8055765

The fix was tested locally on Linux with the jtreg "-ignore:run" flag.

Thanks.

-George