Group tests by class
Group tests by class

It guarantees that all tests inside the test class will be executed in
sigle thread. It makes us able to group some tests that uses same
external resource into one tests execution thread to avoid races.
Example: tests that are use external MySQL/PostgreSQL.

Change-Id: I67f10d20ea84caa9335f909fb5f30da4b4e7f1ca

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