Use j.l.ThreadGroup class directly for GetThreadGroupInfo

We were using the class of the input to GetThreadGroupInfo in some
situations. This could lead to us reading the wrong field or not
finding expected fields. Change to always directly use the
j.l.ThreadGroup class from WellKnownClasses. Also use some handles in
this function.

Test: ./test.py --host
Bug: 140521090
Change-Id: I3560662718311ccc0fa9b906f178407350ce9960
3 files changed