Add AUTHORS, ChangeLog, doc/build/ to gitignore
Add AUTHORS, ChangeLog, doc/build/ to gitignore

These file should be ignored because they are generated by the command, "tox -e docs"

AUTHORS
ChangeLog
doc/build/

Change-Id: I5b9e2adc851800f0391d236d266c33606fc160df
Closes-Bug: 1493670

rajalokan/kolla,mrangana/kolla,rajalokan/kolla,tonyli71/kolla,coolsvap/kolla,openstack/kolla,GalenMa/kolla,coolsvap/kolla,toby82/kolla,tonyli71/kolla,rahulunair/kolla,mandre/kolla,negronjl/kolla,coolsvap/kolla,toby82/kolla,negronjl/kolla,stackforge/kolla,limamauricio/mykolla,dardelean/kolla-ansible,toby82/kolla,nihilifer/kolla,limamauricio/mykolla,fdumpling/kolla,dardelean/kolla-ansible,nihilifer/kolla,intel-onp/kolla,fdumpling/kolla,intel-onp/kolla,mrangana/kolla,fdumpling/kolla,dardelean/kolla-ansible,rahulunair/kolla,mandre/kolla,mandre/kolla,negronjl/kolla,openstack/kolla,limamauricio/mykolla,GalenMa/kolla,stackforge/kolla,rajalokan/kolla,stackforge/kolla