SERVER-15623 Add all RS member states as ReplSetTest constants.

Signed-off-by: Matt Kangas <matt.kangas@mongodb.com>
SERVER-15623 Update test of w:0 in getLastErrorDefaults.

As of 0bb7d05 a secondary that refuses the RS config reports
itself "down".

Signed-off-by: Matt Kangas <matt.kangas@mongodb.com>