Move cells job from 'experimental' to 'check'

This was moved to experimental around FF to conserve resources by not
running a non voting job with known issues.  Now that things have slowed
down we'd like to start addressing CI cells issues so we can move
towards gating on it.

Change-Id: Ic32bd65d5eb7656c6383748a9e5ac585c665bda6
Merge "Move cells job from 'experimental' to 'check'"