Only run GentleKill test as root

Without root, Service::Start() fails due to lack of permissions.

Bug: 267559075
Test: run cts -m CtsInitTestCases -t init#GentleKill
      atest init#GentleKill
      Will skip under cts, pass under atest
Change-Id: I69e8be7000718bdba1c2acd9675b5645c0891afc
1 file changed