Clean up .gitignore
Clean up .gitignore

Several files were removed from the doc sources and config, so there are a
few folders in .gitignore, which are not needed anymore. Also there was a
build directory referenced and the only build directory is under the doc
folder, so this was corrected also.

Change-Id: I60f25d282caa813b3bfc790988578b9882ba95ab

idegtiarov/ceilometer,fabian4/ceilometer,ityaptin/ceilometer,MisterPup/Ceilometer-Juno-Extension,sileht/aodh,isyippee/ceilometer,mathslinux/ceilometer,Juniper/ceilometer,idegtiarov/ceilometer,maestro-hybrid-cloud/ceilometer,luogangyi/Ceilometer-oVirt,isyippee/ceilometer,luogangyi/Ceilometer-oVirt,eayunstack/ceilometer,froyobin/ceilometer,m1093782566/openstack_org_ceilometer,redhat-openstack/ceilometer,froyobin/ceilometer,eayunstack/ceilometer,m1093782566/openstack_org_ceilometer,Juniper/ceilometer,cernops/ceilometer,r-mibu/ceilometer,openstack/aodh,openstack/aodh,chungg/aodh,sileht/aodh,redhat-openstack/ceilometer,pkilambi/ceilometer,MisterPup/Ceilometer-Juno-Extension,chungg/aodh,cernops/ceilometer,openstack/ceilometer,pkilambi/ceilometer,r-mibu/ceilometer,fabian4/ceilometer,mathslinux/ceilometer,pczerkas/aodh,ityaptin/ceilometer,pczerkas/aodh,maestro-hybrid-cloud/ceilometer,openstack/ceilometer