Improve help text for exceptions
Improve help text for exceptions

Previous commit moved exceptions option to central location.
This commit adds additional help text to those options.

Blueprint centralize-config-options-newton

Change-Id: I471216fe5828718f979d1ec3a77add8a258e68e5

rahulunair/nova,mikalstill/nova,jianghuaw/nova,alaski/nova,mikalstill/nova,mahak/nova,jianghuaw/nova,klmitch/nova,mikalstill/nova,sebrandon1/nova,sebrandon1/nova,alaski/nova,rahulunair/nova,rajalokan/nova,klmitch/nova,rajalokan/nova,vmturbo/nova,vmturbo/nova,hanlind/nova,phenoxim/nova,vmturbo/nova,Juniper/nova,gooddata/openstack-nova,hanlind/nova,jianghuaw/nova,rajalokan/nova,rajalokan/nova,gooddata/openstack-nova,Juniper/nova,gooddata/openstack-nova,openstack/nova,sebrandon1/nova,jianghuaw/nova,Juniper/nova,gooddata/openstack-nova,cloudbase/nova,openstack/nova,openstack/nova,cloudbase/nova,mahak/nova,cloudbase/nova,klmitch/nova,klmitch/nova,rahulunair/nova,hanlind/nova,phenoxim/nova,mahak/nova,vmturbo/nova,Juniper/nova