init is a dynamic executable

init is now a dynamic executable. So it has to be able to execute the
dynamic linker (/system/bin/linker) and shared libraries (e.g.,
/system/lib/libc.so). Furthermore, when in recovery mode, the files are
all labeled as rootfs - because the recovery ramdisk does not support
xattr, so files of type rootfs is allowed to be executed.

Do the same for kernel and ueventd because they are executing the init
executable.

Bug: 63673171
Test: `adb reboot recovery; adb devices` shows the device ID
Change-Id: Ic6225bb8e129a00771e1455e259ff28241b70396