Additional ACLs for the system subshell commands

By default the following roles are required with this change:
  system:property - admin
  system:shutdown - admin
  system:start-level
   - viewer can obtain current start level
   - manager can set start levels >= 100
   - admin can only set start levels < 100


git-svn-id: https://svn.apache.org/repos/asf/karaf/trunk@1546018 13f79535-47bb-0310-9956-ffa450edef68