RFR JDK-8210243: [TEST] rewrite com/sun/jdi shell tests to java version - step3

[Alex Menkov]

Hi all,

Please review a fix for
https://bugs.openjdk.java.net/browse/JDK-8210243
webrev:
http://cr.openjdk.java.net/~amenkov/sh2java/step3/webrev.01/
The fix converts the following tests:
- test/jdk/com/sun/jdi/JdbArgTest.sh
- test/jdk/com/sun/jdi/JdbLockTest.sh
- test/jdk/com/sun/jdi/JdbMissStep.sh
- test/jdk/com/sun/jdi/JdbVarargsTest.sh
- test/jdk/com/sun/jdi/MixedSuspendTest.sh
- test/jdk/com/sun/jdi/NotAField.sh
- test/jdk/com/sun/jdi/NullLocalVariable.sh

JdbArgTest requires to run only jdb (without debuggee), so Jdb class was 
decoupled - it now contains only jdb logic, debuggee logic was moved to 
JdbTest.

--alex