Fix slow specs in roadmap

What does this MR do?

Fix slow specs in roadmap_app_spec by:

• Moving the store setup to before the component
• Slicing the epics passed to the store, since a full mount with lots of epics seemed to take a long time.

Screenshots

Before	After

Follow up

We shouldn't ignore the fact that there is some per-epic slowness. Created a follow-up issue to address this #217140.

References

• Closes #217012 (closed)