Update cells v2 layout doc caveats for Queens
Update cells v2 layout doc caveats for Queens

The instance list performance and reschedules issues have
been fixed in Queens so this updates the caveats section
of the cells v2 layout doc to point out those changes since
Pike.

Change-Id: I882f185554b6d2781534fa93e41e5010ea3a641d

mikalstill/nova,klmitch/nova,klmitch/nova,openstack/nova,rahulunair/nova,klmitch/nova,mikalstill/nova,gooddata/openstack-nova,gooddata/openstack-nova,phenoxim/nova,rahulunair/nova,mahak/nova,mahak/nova,openstack/nova,rahulunair/nova,mahak/nova,mikalstill/nova,gooddata/openstack-nova,klmitch/nova,openstack/nova,gooddata/openstack-nova,phenoxim/nova