Fix potential use-after-free bug in reboot

Instead of operating on raw pointers, init now uses name of the
services as it's primary identifier. Only place that still uses
vector<Service*> is StopServices.

In addition, ServiceList::services() function is removed, which should
help avoiding similar bugs in the future.

Bug: 170315126
Bug: 174335499
Test: adb reboot
Test: atest CtsInitTestCases
Change-Id: I73ecd7a8c58c2ec3732934c595b7f7db814b7034
Merged-In: I73ecd7a8c58c2ec3732934c595b7f7db814b7034
(cherry picked from commit bbba64826fdfb7be1f04b7bbb125fbe6d25e5028)