Add /data/security path for mac_permissions.xml.

/data/security is now the preferred location for updated policy files.
Add it for mac_permissions.xml.
Separate change will remove the old /data/system location.

Change-Id: I2774661e84c858c9b698ec60e224bbbcdac732f3
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>