validate.py variable changes

added ,'bk001-ch003-associate-general.xml' to FILE_EXCEPTIONS and removed 'openstack-training' from BOOK_EXCEPTIONS. validate.py was failing  http://logs.openstack.org/50/40550/1/check/gate-openstack-manuals-validate/e3d606e/console.html.gz. As per Lorin, next step may be to remove individual file validation altogether

Change-Id: Ibd865730c1f17d221a5d783fd65b2c8ba2f567cc
Merge "validate.py variable changes"