Cleanup ServiceState.toString()

Updating the formatting of the toString() method to
name the fields that it's printing, and to use one of
the more common formats for object dumping.

Bug: 64300932
Test: compilation, dumpsys
Merged-In: I56c4679d2a4a184f659870481e2ce0699fe38613
Change-Id: I56c4679d2a4a184f659870481e2ce0699fe38613
(cherry picked from commit 9acfe6f9)