Logout setting of cookie breaks upgrade from pre 1.9 to 1.9+ (Bug #1353153)

If the user who is upgrading the site is logged into the site and is a
member of a normal (not mahara) institution it causes the upgrade to
break because the upgrade process tries to log them out and logout()
function tries to set a cookie and the cookie needs info from the
config_institution table and it doesn't exist yet.

Change-Id: Ib8bb83fc1b774cec5636af6009ebf9906349bca3
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>
Merge "Logout setting of cookie breaks upgrade from pre 1.9 to 1.9+ (Bug #1353153)"