Add Mesos into supported orchestrations

[suntech-lab]

Mesos is supported by TF. Please add it into supported orchestrations on the front page.

[vmbrasseur]

Thanks, @tonyliu0592. We now have some more information about this:

From the product team: "Although we have added Mesosphere…for this release, we are not continuing support…"

They recommend it not be included in websites or other promotional material, so we won't be adding it to the site.