stable/create-release-tracker: change parsing of bug tasks
Current bug_target_name in bug tasks is returning the value of the
project's display_name property. This is breaking create-release-tracker
parsing on main launchpad (production), because the project display name
there contain spaces ('Kernel SRU Workflow'). Fix this by using
display_name property of the kernel-sru-workflow project when getting
the task names for assignment.