Reduce shell power over user management.

Remove MANAGE_USERS permission from shell and whitelist it for
some specific functionality.

Bug: 29189712
Change-Id: Ifb37448c091af91991964511e3efb1bb4dea1ff3
diff --git a/core/res/AndroidManifest.xml b/core/res/AndroidManifest.xml
index b03ba20..5e58327 100644
--- a/core/res/AndroidManifest.xml
+++ b/core/res/AndroidManifest.xml
@@ -1621,6 +1621,14 @@
     <permission android:name="android.permission.MANAGE_USERS"
         android:protectionLevel="signature|privileged" />
 
+    <!-- @hide Allows an application to create, remove users and get the list of
+         users on the device. Applications holding this permission can only create restricted,
+         guest, managed, and ephemeral users. For creating other kind of users,
+         {@link android.Manifest.permission#MANAGE_USERS} is needed.
+         This permission is not available to third party applications. -->
+    <permission android:name="android.permission.CREATE_USERS"
+        android:protectionLevel="signature" />
+
     <!-- @hide Allows an application to set the profile owners and the device owner.
          This permission is not available to third party applications.-->
     <permission android:name="android.permission.MANAGE_PROFILE_AND_DEVICE_OWNERS"