dbus_utility_test: fix test case names

This commit applies the GTest test case naming convention: Camel case,
use decriptive Test names.

It also groups test cases according to the name.

Reference:
https://testing.googleblog.com/2014/10/testing-on-toilet-writing-descriptive.html
http://google.github.io/googletest/primer.html#simple-tests



Tested: unit test passes.

Signed-off-by: Nan Zhou <nanzhoumails@gmail.com>
Change-Id: Ibd1bfcb4456b64e43f437cc2afa7464f03ee634c