Split the marketplace manifest

This is a precursor to splitting marketplace tests out into their own repo.

We're splitting this out into its own job on Jenkins (as suggested a few weeks ago) and we can include the (unreliable) payment tests in this manifest without influencing the Gaia smoke tests.

These tests don't really need to run on master and it will be easier for us to target them to a specific CI node if we get the 'magic' SIM card that we want!