Add reboot_test

This test spawns several services backed by /system/bin/yes executable,
and then stops them either while SIGTERM or SIGKILL.

Ideally we want to unit test more of reboot logic, but that requires a
bigger refactoring.

Test: atest CtsInitTestCases
Bug: 170315126
Bug: 174335499
Change-Id: Ife48b1636c6ca2d0aac73f4eb6f4737343a88e7a
diff --git a/init/reboot.cpp b/init/reboot.cpp
index 409f8cb..90b565c 100644
--- a/init/reboot.cpp
+++ b/init/reboot.cpp
@@ -533,8 +533,8 @@
 
 // Like StopServices, but also logs all the services that failed to stop after the provided timeout.
 // Returns number of violators.
-static int StopServicesAndLogViolations(const std::set<std::string>& services,
-                                        std::chrono::milliseconds timeout, bool terminate) {
+int StopServicesAndLogViolations(const std::set<std::string>& services,
+                                 std::chrono::milliseconds timeout, bool terminate) {
     StopServices(services, timeout, terminate);
     int still_running = 0;
     for (const auto& s : ServiceList::GetInstance()) {