Make deleting transient clusters safe
Make deleting transient clusters safe

We want Sahara to be able to run distributed. I.e. several sahara-api
and sahara-engine should run in parallel and the whole setup should
work fine. For that to work we need to make deleting periodic clusters
safe, since a cluster could be deleted by two engines simultaneously.

Partially Implements: blueprint scalable-savanna
Change-Id: I33f9813ba58a4cca7d0221f518c29f8e605cc999

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