Increase min-ready for tripleo-f20 nodes

These should be created at a ratio of 5:1 with the tripleo-precise
nodes as we have 5 jobs running on precise for every 1 on f20. When
the jenkins configs were moved to a single global section
Ide8a4026967ad536f6fe21e52694ee746950fb48
min-ready was increased to reflect a new global number for
tripleo-precise nodes but tripleo-f20 images were left at 1.

Change-Id: I0e1eb3dae54d217ea37f1e5a3ff9dedfb1e50c0c
Merge "Increase min-ready for tripleo-f20 nodes"