PowerManagerService: Don't reboot directly.

Instead of calling the reboot system call ourselves, send
a message to init asking it to reboot the system. Init is in
a better position to make sure the system is cleanly shutdown.

Get rid of CAP_SYS_BOOT from system_server.

Bug: 8646621
Change-Id: I200722412844ad8d99e35a442021c6263c3ebc05

core/java/com/android/internal/os/ZygoteInit.java

@@ -479,7 +479,6 @@ public class ZygoteInit {
             OsConstants.CAP_NET_BIND_SERVICE,
             OsConstants.CAP_NET_BROADCAST,
             OsConstants.CAP_NET_RAW,
-            OsConstants.CAP_SYS_BOOT,
             OsConstants.CAP_SYS_MODULE,
             OsConstants.CAP_SYS_NICE,
             OsConstants.CAP_SYS_RESOURCE,