Modify default file/directory permissions

* Remove execute permission on regular files (PRIV_PERMS).
* Create file mode constants for public/private directory/file.
* Grant read access to group members for files/directores marked private.

Change-Id: I92563a125e6ac93762db5fda65412f9a68ef35e3
Fixes: bug #1206254
Merge "Modify default file/directory permissions"