multinode min ready 2

Two experimental job have been defined for
as d-g experimental job, but we just keep ready
only 1 pair of nodes. It can cause longer wait
time on the d-g experimental checks.

Increasing the min-ready on devstack-trusty-2-node
from 1 to 2.

Change-Id: I7a51efa9dfbe45264819960da74ab5b8d9874426
Merge "multinode min ready 2"