<Swing Dev> [9] Review request for 8165207: [macosx] Test javax/swing/Popup/TaskbarPositionTest.java fails on Mac 10.12

[Александр Попов]

Hello,
review my changes please.

Fix for https://bugs.openjdk.java.net/browse/JDK-8165207: 
Webrev:http://cr.openjdk.java.net/~avstepan/8165207/webrev.01/
Issue: https://bugs.openjdk.java.net/browse/JDK-8165207

This is a test bug. On Aqua LaF JCombobox popup could appear both upper label and arrow and lower.  
So - check for its coordinates does not make sense. Also fixed Ctrl-down shortcut. It is invalid - it is special shortcut for OS X. Down key is enough to expand combobox.
Tested on Mac OS X with different LaFs - Aqua, Nimbus, Metal. Works perfectly after fix.
I used jdk 9b144 for testing.

-- 
Best regards,
Alexander.