update .gitignore
update .gitignore

Ignore build/ directory, which is auto-created when running `python
setup.py bdist` like dist/ directory.

Change-Id: Ie58936320d995e4e81f8929128475e538665bde8

prashanthpai/swift,williamthegrey/swift,hurricanerix/swift,sarvesh-ranjan/swift,dpgoetz/swift,hurricanerix/swift,aerwin3/swift,mjzmjz/swift,zaitcev/swift-lfs,mjzmjz/swift,aerwin3/swift,nadeemsyed/swift,daasbank/swift,daasbank/swift,tipabu/swift,openstack/swift,xiaoguoai/ec-dev-swift,IPVL/swift-kilo,redhat-openstack/swift,wenhuizhang/swift,eatbyte/Swift,Em-Pan/swift,dpgoetz/swift,citrix-openstack-build/swift,clayg/swift,hurricanerix/swift,JioCloud/swift,zackmdavis/swift,Khushbu27/Tutorial,citrix-openstack/build-swift,smerritt/swift,revoer/keystone-8.0.0,psachin/swift,tipabu/swift,tipabu/swift,psachin/swift,bkolli/swift,tipabu/swift,AfonsoFGarcia/swift,eatbyte/Swift,hbhdytf/mac,IPVL/swift-kilo,redhat-openstack/swift,zackmdavis/swift,dencaval/swift,hbhdytf/mac2,smerritt/swift,notmyname/swift,redbo/swift,bradleypj823/swift,swiftstack/swift,hurricanerix/swift,smerritt/swift,mjwtom/swift,hbhdytf/mac,larsbutler/swift,nadeemsyed/swift,sarvesh-ranjan/swift,matthewoliver/swift,orion/swift-config,matthewoliver/swift,prashanthpai/swift,notmyname/swift,nadeemsyed/swift,notmyname/swift,clayg/swift,JioCloud/swift,dencaval/swift,scality/ScalitySproxydSwift,smerritt/swift,clayg/swift,redbo/swift,shibaniahegde/OpenStak_swift,anishnarang/gswift,levythu/swift,Seagate/swift,openstack/swift,bkolli/swift,tsli/test,nadeemsyed/swift,takeshineshiro/swift,levythu/swift,gold3bear/swift,williamthegrey/swift,tsli/test,Akanoa/swift,notmyname/swift,openstack/swift,NeCTAR-RC/swift,thiagodasilva/swift,Khushbu27/Tutorial,hbhdytf/mac2,maginatics/swift,citrix-openstack/build-swift,bradleypj823/swift,wenhuizhang/swift,orion/swift-config,Seagate/swift,bouncestorage/swift,swiftstack/swift,Akanoa/swift,maginatics/swift,iostackproject/IO-Bandwidth-Differentiation,zaitcev/swift-lfs,Em-Pan/swift,NeCTAR-RC/swift,takeshineshiro/swift,thiagodasilva/swift,swiftstack/swift,larsbutler/swift,AfonsoFGarcia/swift,mjwtom/swift,psachin/swift,bouncestorage/swift,hbhdytf/mac2,rackerlabs/swift,psachin/swift,openstack/swift,citrix-openstack-build/swift,gold3bear/swift,clayg/swift,xiaoguoai/ec-dev-swift,matthewoliver/swift,revoer/keystone-8.0.0,anishnarang/gswift,matthewoliver/swift,shibaniahegde/OpenStak_swift,rackerlabs/swift,iostackproject/IO-Bandwidth-Differentiation,scality/ScalitySproxydSwift,hbhdytf/mac2