LP#1552060: fix persistent login

LP#1552060: fix persistent login

This patch makes open-ils.auth_internal look for
default_timeout values for persistent authentication
in the intended section of opensrf.xml.

To test:

[1] Attempt to log into the public catalog with the "Stay logged in?"
    option in effect.  The login will either fail or the session
    will not persist when navigating within the "My Account"
    pages.
[2] Apply the patch and restart services.
[3] Attempt step 1 again; this time, authentication should work
    and the session should remain active.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>