Fix issue in labelling files

The current version of security manager put this tags

 - SECURITY_MANAGER_PATH_PRIVATE
 - SECURITY_MANAGER_PATH_RW

      User::App::XXXX

 - SECURITY_MANAGER_PATH_PUBLIC
 - SECURITY_MANAGER_PATH_RO

      User::Home

 - SECURITY_MANAGER_PATH_PUBLIC_RO

      _ (underscore or floor)

Putting floor is bad because it produces
files and directories that can't be removed.

Using SECURITY_MANAGER_PATH_RO instead of
SECURITY_MANAGER_PATH_PUBLIC_RO sets the
label "User::Home". It is valid because this
label is already read only for applications.
But it is writable by the "System" labelled
services at the opposite of "_".

Change-Id: I685fe366fddb95858c66b827e28acf6d005bcfc0
Signed-off-by: José Bollo <jose.bollo@iot.bzh>