Add userspace_reboot_test_prop

This property type represents properties used in CTS tests of userspace
reboot. For example, test.userspace_reboot.requested property which is
used to check that userspace reboot was successful and didn't result in
full reboot, e.g.:
* before test setprop test.userspace_reboot.requested 1
* adb reboot userspace
* wait for boot to complete
* verify that value of test.userspace_reboot.requested is still 1

Test: adb shell setprop test.userspace_reboot.requested 1
Bug: 150901232
Change-Id: I45d187f386149cec08318ea8545ab864b5810ca8
Merged-In: I45d187f386149cec08318ea8545ab864b5810ca8
(cherry picked from commit 3bd53a9ceecc37c79090c59776408b3d4733b036)
diff --git a/private/shell.te b/private/shell.te
index 2c69f95..76ff073 100644
--- a/private/shell.te
+++ b/private/shell.te
@@ -73,6 +73,10 @@
 set_prop(shell, lpdumpd_prop);
 binder_call(shell, lpdumpd)
 
+# Allow shell to set and read value of properties used for CTS tests of
+# userspace reboot
+set_prop(shell, userspace_reboot_test_prop)
+
 # Allow shell to get encryption policy of /data/local/tmp/, for CTS
 allowxperm shell shell_data_file:dir ioctl {
   FS_IOC_GET_ENCRYPTION_POLICY