Update requirements to the latest versions
Update requirements to the latest versions

* pbr 0.5.21 includes all savanna-related fixes
* next major release of sqlalchemy allowed

Change-Id: Ib47408dc217fad1c97b623ce0557d9d4f6da0e16

egafford/sahara,bigfootproject/sahara,mapr/sahara,crobby/sahara,citrix-openstack-build/sahara,henaras/sahara,bigfootproject/sahara,tellesnobrega/storm_plugin,matips/iosr-2015,xme1226/sahara,redhat-openstack/sahara,mapr/sahara,egafford/sahara,matips/iosr-2015,ekasitk/sahara,tellesnobrega/sahara,zhujzhuo/Sahara,esikachev/scenario,keedio/sahara,ekasitk/sahara,rnirmal/savanna,rnirmal/savanna,xme1226/sahara,esikachev/sahara-backup,keedio/sahara,zhangjunli177/sahara,xme1226/sahara,matips/iosr-2015,redhat-openstack/sahara,citrix-openstack-build/sahara,esikachev/scenario,henaras/sahara,zhangjunli177/sahara,bigfootproject/sahara,citrix-openstack-build/sahara,zhangjunli177/sahara,openstack/sahara,tellesnobrega/sahara,esikachev/sahara-backup,tellesnobrega/storm_plugin,tellesnobrega/storm_plugin,redhat-openstack/sahara,mapr/sahara,crobby/sahara,esikachev/scenario,esikachev/sahara-backup,crobby/sahara,keedio/sahara,openstack/sahara,ekasitk/sahara,henaras/sahara,zhujzhuo/Sahara,zhujzhuo/Sahara