RFR 8211736: jdb doesn't print prompt when breakpoint is hit and suspend policy is STOP_EVENT_THREAD

[Daniil Titov]

Please review the change that fixes the issue with missing prompt in jdb when a breakpoint is hit and the suspend policy is set to stop the thread only.

Webrev: http://cr.openjdk.java.net/~dtitov/8211736/webrev.01
Issue: https://bugs.openjdk.java.net/browse/JDK-8211736

Thanks!
--Daniil