[failure mode] revisions that fail to scale up from 0 should set Ready=False

[dprotaso]

trafficstars

After a successful initial deploy and scale to zero - if a revision were to fail to scale from 0 a second time we should mark Ready=False.

This intent of this issue is to confirm what is the current behaviour is when readiness & liveness probes fail.

[julz]

/area api /kind spec /triage accepted

[psschwei]

/assign

[psschwei]

whoops, was in the wrong tab /unassign